A Doctor of Philosophy (PhD or DPhil) is a type of doctorate degree awarded by universities in many countries. The degree, named after its historic roots as a Doctorate licensed to one allowed to profess a Philosophia, was formally awarded by European universities since the Medieval era circa 1150-1200. PhDs are awarded for a wide range of programs in the sciences (e.g., biology, physics, mathematics, etc.), engineering, and humanities (e.g., history, English literature, musicology, etc.). The PhD is a terminal degree in many fields. The completion of a PhD is a requirement for employment as a university professor, researcher, or scientist in many fields. A clear distinction is made between an "earned doctorate", which is awarded for completion of a course of study and thesis or dissertation and an "honorary doctorate", which is an honorary title granted by a university to a successful or notable person.
The PhD degree varies considerably according to the country, institution, and time period, from entry-level research degrees to higher doctorates. A person who attains a doctorate of philosophy is automatically awarded the academic title of doctor. During the studies that lead to the degree, the student is called doctoral student or PhD student, but also "doctoral candidate" or "PhD candidate" once the student has completed all of the coursework and comprehensive examinations and is working on their thesis or dissertation.
A PhD candidate must submit a project, thesis or dissertation often consisting of a body of original academic research, which is in principle worthy of publication in a peer-reviewed journal. In many countries a candidate must defend this work before a panel of expert examiners appointed by the university. Universities award other types of doctorates besides the PhD, such as the Doctor of Musical Arts (DMA), a degree for music performers and the Doctor of Education (Ed.D.), a degree for professional educators.
In the context of academic degrees, the term "philosophy" does not refer solely to the field or academic discipline of philosophy, but is used in a broader sense in accordance with its original Greek meaning, which is "love of wisdom". In most of Europe, all fields (history, philosophy, social sciences, mathematics and natural philosophy/natural sciences) other than theology, law, and medicine (the so-called professional, vocational, or technical curriculum) were traditionally known as philosophy, and in Germany and elsewhere in Europe the basic faculty of liberal arts was known as the "faculty of philosophy".
In the universities of Medieval Europe, study was organized in four faculties: the basic faculty of arts, and the three higher faculties of theology, medicine, and law (canon law and civil law). All of these faculties awarded intermediate degrees (bachelor of arts, of theology, of laws, of medicine) and final degrees. Initially, the titles of master and doctor were used interchangeably for the final degrees—being that the title Doctor merely was a formality bestowed on a Teacher/Master of the art—but by the late Middle Ages the terms Master of Arts and Doctor of Theology/Divinity, Doctor of Law, and Doctor of Medicine had become standard in most places (though in the German and Italian universities the term Doctor was used for all faculties). The doctorates in the higher faculties were quite different from the current Ph.D. degree in that they were awarded for advanced scholarship, not original research. No dissertation or original work was required, only lengthy residency requirements and examinations. Besides these degrees, there was the licentiate. Originally this was a license to teach, awarded shortly before the award of the master or doctor degree by the diocese in which the university was located, but later it evolved into an academic degree in its own right, in particular in the continental universities.
In theory the full course of studies might lead in succession to the degrees of, e.g., Bachelor of Arts, Licentiate of Arts, Master of Arts, Bachelor of Medicine, Licentiate of Medicine, Doctor of Medicine. There were many exceptions to this, however. Most students left the university before becoming masters of arts, whereas regulars (members of monastic orders) could skip the arts faculty entirely.
Educational reforms in Germany
This situation changed in the early 19th century through the educational reforms in Germany, most strongly embodied in the model of the University of Berlin, founded and controlled by the Prussian government in 1810. The arts faculty, which in Germany was labelled the faculty of philosophy, started demanding contributions to research, attested by a dissertation, for the award of their final degree, which was labelled Doctor of Philosophy (abbreviated as Ph.D.)—originally this was just the German equivalent of the Master of Arts degree. Whereas in the Middle Ages the arts faculty had a set curriculum, based upon the trivium and the quadrivium, by the 19th century it had come to house all the courses of study in subjects now commonly referred to as sciences and humanities. Professors across the humanities and Sciences focused on their advanced research. Practically all the funding came from the central government, and could be cut off if the professor was politically unacceptable.
These reforms proved extremely successful, and fairly quickly the German universities started attracting foreign students, notably from the United States. The American students would go to Germany to obtain a Ph.D. after having studied for a bachelor's degrees at an American college. So influential was this practice that it was imported to the United States, where in 1861 Yale University started granting the Ph.D. degree to younger students who, after having obtained the bachelor's degree, had completed a prescribed course of graduate study and successfully defended a thesis or dissertation containing original research in science or in the humanities. This research degree of doctor of philosophy was the first to be given in North America. Even though in Germany the name of the doctorate was adapted accordingly after the philosophy faculty started being split up − e.g. Dr. rer. nat. for doctorates in the faculty of natural sciences − in most of the English-speaking world the name of Doctor of Philosophy was retained for research doctorates in all disciplines.
The doctorate in the United Kingdom
The Ph.D. degree spread to Canada in 1901, and then to Great Britain in 1917. In particular in the English universities the introduction of the research doctorate largely happened to compete with Germany for American students, but the initiative was first halted by internal criticism. In first instance, in particular at the University of London (from about 1860 onwards), the degrees of Doctor of Science (DSc) and Doctor of Literature (DLit) were introduced, which could be awarded upon presentation of a thesis containing original work. This involved no research training however, and did not have the desired effect of attracting foreign research students. Finally in 1917 the current degree of Ph.D. was introduced, along the lines of the American and German model, and quickly became popular with both British and foreign students. The slightly older degrees of Doctor of Science and Doctor of Literature/Letters still exist in British universities; together with the much older degrees of Doctor of Divinity (DD), Doctor of Music (DMus), Doctor of Civil Law (DCL) and Doctor of Medicine (MD) they form the higher doctorates, but apart from honorary degrees they are only infrequently awarded.
It should be noted that in the English (but not the Scottish) universities the Faculty of Arts had become dominant by the early 19th century. Indeed, the higher faculties had largely atrophied, since medical training had shifted to teaching hospitals, the legal training for the common law system was provided by the Inns of Court (with some minor exceptions, see Doctors' Commons), and few students undertook formal study in theology. This is contrast with the situation in the continental European universities at the time, where the preparatory role of the Faculty of Philosophy or Arts was to a great extent taken over by secondary education, as is testified by the ongoing use to this day of the degree of Baccalaureat in France as the qualification obtained after secondary studies. The reforms at the Humboldt University transformed the Faculty of Philosophy or Arts (and its more recent successors such as the Faculty of Sciences) from a lower faculty into one on par with the Faculties of Law and Medicine. A similar evolution happened in many other continental European universities, and at least until reforms in the early 21st century many European countries (e.g. Belgium, Spain and the Scandinavian countries) had in all faculties triple degree structures of bachelor (or candidate) − licentiate − doctor as opposed to bachelor − master − doctor; the meaning of the different degrees varied a lot from country to country however. To this day this is also still the case for the pontifical degrees in theology and canon law: for instance, in Sacred theology the degrees are Bachelor of Sacred Theology (STB), Licentiate of Sacred Theology (STL), and Doctor of Sacred Theology (STD), and in Canon law: Bachelor of Canon Law (JCB), Licentiate of Canon Law (JCL), and Doctor of Canon Law (JCD).
The doctorate in the United States
Until the mid-19th century, advanced degrees were not a criterion for professorships at most colleges. That began to change as the more ambitious scholars at major schools went to Germany for 1 to 3 years to obtain a Ph.D. in the sciences or humanities. Graduate schools slowly emerged in the United States. In 1861, Yale awarded the first three Ph.D.s in North America to Eugene Schuyler, Arthur Williams Wright, and James Morris Whiton. In the next two decades, NYU, the University of Pennsylvania, Harvard, and Princeton also began granting the degree. Major shifts toward graduate education were foretold by the opening of Clark University in 1887, which only offered graduate programs, and the Johns Hopkins University which focused on its Ph.D. program. By the 1890s, Harvard, Columbia, Michigan and Wisconsin were building major graduate programs, whose alumni were hired by new research universities. By 1900, 300 Ph.D.'s were awarded annually, most of them by six universities. It was no longer necessary to study in Germany.
In Germany, the national government funded the universities and the research programs of the leading professors. It was impossible for professors who were not approved by Berlin to train graduate students. In the United States, by contrast, private universities and state universities alike were independent of the federal government. Independence was high, but funding was low. The breakthrough came from private foundations, which began regularly supporting research in science and history; large corporations sometimes supported engineering programs. The postdoctoral fellowship was established by the Rockefeller Foundation in 1919. Meanwhile, the leading universities, in cooperation with the learned societies, set up a network of scholarly journals. "Publish or perish" became the formula for faculty advancement in the research universities. After World War II, state universities across the country expanded greatly in undergraduate enrollment, and eagerly added research programs leading to masters or doctorate degrees. Their graduate faculties had to have a suitable record of publication and research grants. Late in the 20th century, "publish or perish" became increasingly important in colleges and smaller universities.
Detailed requirements for the award of a Ph.D. degree vary throughout the world and even from school to school. It is usually required for the student to hold an Honours degree or a Master's Degree with high academic standing, in order to be considered for a Ph.D. program. In the US, Canada, India and Denmark, for example, many universities require coursework in addition to research for Ph.D. degrees. In other countries (such as the UK) there is generally no such condition, though this varies by university and field. Some individual universities or departments specify additional requirements for students not already in possession of a bachelor's degree or equivalent or higher. In order to submit a successful Ph.D. admission application, copies of academic transcripts, letters of recommendation, a research proposal and a personal statement are often required. Most universities also invite for a special interview before admission.
A candidate must submit a project or thesis or dissertation often consisting of a body of original academic research, which is in principle worthy of publication in a peer-reviewed context. In many countries a candidate must defend this work before a panel of expert examiners appointed by the university; in other countries, the dissertation is examined by a panel of expert examiners who stipulate whether the dissertation is in principle passable and any issues that need to be addressed before the dissertation can be passed.
A Ph.D. student or candidate is conventionally required to study on campus under close supervision. With the popularity of distance education and e-learning technologies, some universities now accept students enrolled into a distance education part-time mode.
In a "sandwich Ph.D." program, Ph.D. candidates do not spend their entire study period at the same university. Instead, the Ph.D. candidates spend the first and last periods of the program at their home universities, and in between conduct research at another institution or field research. Occasionally a "sandwich Ph.D." will be awarded by two universities.
A PhD confirmation is a preliminary presentation or lecture that a PhD candidate presents to faculty and possibly other interested members. The lecture follows after a suitable topic has been identified, and can include such matters as the aim of the research, methodology, first results, planned (or finished) publications, etc.
The confirmation lecture can be seen as a trial run for the final public defense, though faculty members at this stage can still largely influence the direction of the research. At the end of the lecture, the PhD candidate can be seen as "confirmed" - faculty members give their approval and trust that the study is well directed and will with high probability result in the candidate being successful.
Value and criticism
Ph.D. students are often motivated to pursue the Ph.D. by scientific and humanistic curiosity, the desire to contribute to the academic community, service to others, or personal development. A career in academia generally requires a Ph.D., though in some countries, it is possible to reach relatively high positions without a doctorate. In North America, professors are increasingly being required to have a Ph.D., because the percentage of faculty with a Ph.D. is used as a university ratings measure.
The motivation may also include increased salary, but in many cases this is not the result. Research by Casey suggests that, over all subjects, Ph.D.s provide an earnings premium of 26%, but notes that master's degrees provide a premium of 23% already. While this is a small return to the individual (or even an overall deficit when tuition and lost earnings during training are accounted for), he claims there are significant benefits to society for the extra research training. However, some research suggests that overqualified workers are often less satisfied and less productive at their jobs. These difficulties are increasingly being felt by graduates of professional degrees, such as law school, looking to find employment. Ph.D. students often have to take on debt to undertake their degree.
A Ph.D. is also required in some positions outside academia, such as research jobs in major international agencies. In some cases, the Executive Directors of some types of foundations may be expected to hold a Ph.D. In the article "The Peril of Credential Creep in Foreign Policy", it is stated that "[m]ore and more foreign policy professionals are required to hold master's or Ph.D. degrees to compete in their field." The article states that "If having a master's degree at the minimum is de rigueur in Washington's foreign policy world, it is no wonder many are starting to feel that the Ph.D. is a necessary escalation, another case of costly signaling to potential employers." An article on the Australian public service states that "credentialism in the public service is seeing a dramatic increase in the number of graduate positions going to Ph.D.s and masters degrees [are] becoming the base entry level qualification."
The Economist published an article citing various criticisms against the state of Ph.D.s. Richard B. Freeman explains that, based on pre-2000 data, at most only 20% of life science Ph.D. students end up getting jobs specifically in research. In Canada, where the overflow of Ph.D. degree holders is not as severe, 80% of postdoctoral research fellows earn less than or equal to the average construction worker (roughly $38,000 a year) during their postdoctoral research tenure. Only in the fastest developing countries (e.g. China or Brazil) is there a shortage of Ph.D.s.
Higher education systems often offer little incentive to move students through Ph.D. programs quickly, and may even provide incentive to slow them down. To counter this, the United States introduced the Doctor of Arts degree in 1970 with seed money from the Carnegie Foundation for the Advancement of Teaching. The aim of the Doctor of Arts degree was to shorten the time needed to complete the degree by focusing on pedagogy over research, although the Doctor of Arts still contains a significant research component. Germany is one of the few nations engaging these issues, and it has been doing so by reconceptualising Ph.D. programs to be training for careers, outside academia, but still at high-level positions. This development can be seen in the extensive number of Ph.D. holders, typically from the fields of law, engineering and economics, at the very top corporate and administrative positions. To a lesser extent, the UK research councils have tackled the issue by introducing, since 1992, the EngD.
Mark C. Taylor opines that total reform of Ph.D. programs in almost every field is necessary in the U.S., and that pressure to make the necessary changes will need to come from many sources (students, administrators, public and private sectors, etc.). These issues and others are discussed in an April 2011 issue of the journal Nature.
In German-speaking nations; most Eastern European nations; successor states of the former Soviet Union; most parts of Africa, Asia, and many Spanish-speaking countries, the corresponding degree to a Doctor of Philosophy is simply called "Doctor" (Doktor), and the subject area is distinguished by a Latin suffix (e.g., "Dr. med." for Doctor medicinae, Doctor of Medicine; "Dr. rer. nat." for Doctor rerum naturalium, Doctor of the Natural Sciences; "Dr. phil." for Doctor philosophiae, Doctor of Philosophy; "Dr. iur." for Doctor iuris, Doctor of Laws).
Degrees around the globe
The UNESCO, in its International Standard Classification of Education (ISCED), states that "Programmes to be classified at ISCED level 8 are referred to in many ways around the world such as Ph.D., D.Phil., D.Litt., D.Sc., LL.D., Doctorate or similar terms. However, it is important to note that programmes with a similar name to "doctor" should only be included in ISCED level 8 if they satisfy the criteria described in Paragraph 263. For international comparability purposes, the term "doctoral or equivalent" is used to label ISCED level 8".
In Argentina, the admission to a Ph.D. program at public Argentine University requires the full completion of a Master's degree or a Licentiate's degree. Non-Argentine Master's titles are generally accepted into a Ph.D. program when the degree comes from a recognized university.
While a significant portion of postgraduate students finance their tuition and living costs with teaching or research work at private and state-run institutions, international institutions, such as the Fulbright Program and the Organization of American States (OAS), have been known to grant full scholarships for tuition with apportions for housing.
Requirements for completion
Upon completion of at least two years' research and course work as a graduate student, a candidate must demonstrate truthful and original contributions to his or her specific field of knowledge within a frame of academic excellence. The doctoral candidate's work should be presented in a dissertation or thesis prepared under the supervision of a tutor or director, and reviewed by a Doctoral Committee. This Committee should be composed of examiners that are external to the program, and at least one of them should also be external to the institution. The academic degree of Doctor, respective to the correspondent field of science that the candidate has contributed with original and rigorous research, is received after a successful defense of the candidate's dissertation.
Admission to a Ph.D. program in Australia requires applicants to demonstrate capacity to undertake research in the proposed field of study. The standard requirement is a bachelor's degree with either first-class or upper second-class honours. Research master's degrees and coursework master's degrees with a 25% research component are usually considered equivalent. It is also possible for research master's degree students to 'upgrade' to Ph.D. candidature after demonstrating sufficient progress.
Ph.D. students are sometimes offered a scholarship to study for their Ph.D. degree. The most common of these are the government-funded Australian Postgraduate Award (APA), which provides a living stipend to students of approximately A$25,800 a year (tax free). APAs are paid for a duration of 3 years, while a 6-month extension is usually possible upon citing delays out of the control of the student. Some universities also fund a similar scholarship that matches the APA amount. Due to a continual increase in living costs, many Ph.D. students are forced to live under the poverty line. In addition to the more common APA and university scholarships, Australian students have other sources of scholarship funding.
Australian citizens, permanent residents and New Zealand citizens are not charged course fees for their Ph.D. or research master's degree, with exception to the student services and amenities fee (SSAF) which is set by each university and typically involves the largest amount allowed by the Australian government. All fees are paid for by the Australian government, except for the SSAF, under the Research Training Scheme. International students and coursework master's degree students must pay course fees, unless they receive a scholarship to cover them.
Requirements for completion
Completion requirements vary. Most Australian Ph.D. programs do not have a required coursework component. The credit points attached to the degree are all in the product of the research, which is usually an 80,000 word thesis that makes a significant new contribution to the field. The Ph.D. thesis is sent to external examiners who are experts in the field of research and who have not been involved in the work. Examiners are nominated by the candidate's university and their identities are often not revealed to the candidate until the examination is complete. A formal oral defence is generally not part of the examination of the thesis, largely because of the distances that would need to be traveled by the overseas examiners. Scholar Bruno Starrs has examined the growing popularity of the in Australia, with particular reference to the discipline of film and TV studies and the proliferation of honorary doctorates.
Admission to a doctoral programme at a Canadian university usually requires completion of a Master's degree in a related field, with sufficiently high grades and proven research ability. In some cases, a student may progress directly from an Honours Bachelor's degree to a Ph.D. program; other programs allow a student to fast-track to a doctoral program after one year of outstanding work in a Master's program (without having to complete the Master's).
An application package typically includes a research proposal, letters of reference, transcripts, and in some cases, a writing sample or Graduate Record Examination scores. A common criterion for prospective Ph.D. students is the comprehensive or qualifying examination, a process that often commences in the second year of a graduate program. Generally, successful completion of the qualifying exam permits continuance in the graduate program. Formats for this examination include oral examination by the student's faculty committee (or a separate qualifying committee), or written tests designed to demonstrate the student's knowledge in a specialized area (see below) or both.
At English-speaking universities, a student may also be required to demonstrate English language abilities, usually by achieving an acceptable score on a standard examination (for example the Test of English as a Foreign Language). Depending on the field, the student may also be required to demonstrate ability in one or more additional languages. A prospective student applying to French-speaking universities may also have to demonstrate some English language ability.
While some students work outside the university (or at student jobs within the university), in some programs students are advised (or must agree) not to devote more than ten hours per week to activities (e.g., employment) outside of their studies, particularly if they have been given funding. For large and prestigious scholarships, such as those from NSERC and FQRNT, this is an absolute requirement.
At some Canadian universities, most Ph.D. students receive an award equivalent to part or all of the tuition amount for the first four years (this is sometimes called a tuition deferral or tuition waiver). Other sources of funding include teaching assistantships and research assistantships; experience as a teaching assistant is encouraged but not requisite in many programs. Some programs may require all Ph.D. candidates to teach, which may be done under the supervision of their supervisor or regular faculty. Besides these sources of funding, there are also various competitive scholarships, bursaries, and awards available, such as those offered by the federal government via NSERC, CIHR, or SSHRC.
Requirements for completion
In general, the first two years of study are devoted to completion of coursework and the comprehensive examinations. At this stage, the student is known as a "Ph.D. student" or "doctoral student". It is usually expected that the student will have completed most of his or her required coursework by the end of this stage. Furthermore, it is usually required that by the end of eighteen to thirty-six months after the first registration, the student will have successfully completed the comprehensive exams.
Upon successful completion of the comprehensive exams, the student becomes known as a "Ph.D. candidate". From this stage on, the bulk of the student's time will be devoted to his or her own research, culminating in the completion of a Ph.D. thesis or dissertation. The final requirement is an oral defense of the thesis, which is open to the public in some, but not all, universities. At most Canadian universities, the time needed to complete a Ph.D. degree typically ranges from four to six years. It is, however, not uncommon for students to be unable to complete all the requirements within six years, particularly given that funding packages often support students for only two to four years; many departments will allow program extensions at the discretion of the thesis supervisor and/or department chair. Alternate arrangements exist whereby a student is allowed to let their registration in the program lapse at the end of six years and re-register once the thesis is completed in draft form. The general rule is that graduate students are obligated to pay tuition until the initial thesis submission has been received by the thesis office. In other words, if a Ph.D. student defers or delays the initial submission of their thesis they remain obligated to pay fees until such time that the thesis has been received in good standing.
In Colombia, the Ph.D. course admission may require a master's degree (Magíster) in some universities, specially public universities. However, it could also be applied for a direct doctorate in specific cases, according to the jury's recommendations on the thesis proposal.
Most of postgraduate students in Colombia must finance their tuition fees by means of teaching assistant seats or research works. Some institutions such as Colciencias, Colfuturo and Icetex grant scholarships or provide awards in the form of forgivable loans 
Requirements for completion
After two or two and a half years it is expected the research work of the doctoral candidate to be submitted in the form of oral qualification, where suggestions and corrections about the research hypothesis and methodology, as well as on the course of the research work are performed. The Ph.D. degree is only received after a successful defense of the candidate's thesis is performed (four or five years after the enrollment), and most of the times also requiring the most important results having been published in at least one peer-reviewed high impact international journal.
In Finland, the degree of filosofian tohtori (abbreviated FT) is awarded by traditional universities, such as University of Helsinki. A Master's degree is required, and the doctorate combines approximately 4–5 years of research (amounting to 3-5 scientific articles, some of which must be first-author) and 60 ECTS points of studies. Other universities such as Aalto University award degrees such as tekniikan tohtori (TkT, engineering), taiteen tohtori (TaT, art), etc., which are translated in English to Doctor of Science (D.Sc.), and they are formally equivalent. The licentiate (filosofian lisensiaatti or FL) requires only 2–3 years of research, and is sometimes done before a FT.
Before 1984 three research doctorates existed in France: the State doctorate (doctorat d'État, the old doctorate introduced in 1808), the third cycle doctorate (doctorat de troisième cycle, created in 1954 and shorter than the State doctorate) and the diploma of doctor-engineer (diplôme de docteur-ingénieur created in 1923), for technical research. After 1984, only one type of doctoral degree remained, called "doctorate" (Doctorat). The latter is equivalent to the Ph.D.
Students pursuing the Ph.D. degree must first complete a master's degree program, which takes two years after graduation with a bachelor's degree (five years in total). The candidate must find funding and a formal doctoral advisor (Directeur de thèse) with an habilitation throughout the doctoral program.
The Masters program is divided into two branches: "master professionnel", which orientates the students towards the working world, and Master of Research (Master-recherche), which is oriented towards research. The Ph.D. admission is granted by a graduate school (in French, "école doctorale"). A Ph.D. Student has to follow some courses offered by the graduate school while continuing his/her research at laboratory. His/her research may be carried out in a laboratory, at a university, or in a company. In the last case, the company hires the student as an engineer and the student is supervised by both the company's tutor and a labs' professor. The validation of the Ph.D. degree requires generally 3 to 4 years after the master's degree.
The financing of Ph.D. studies comes mainly from funds for research of the French Ministry of Higher Education and Research. The most common procedure is a short-term employment contract called doctoral contract: the institution of higher education is the employer and the Ph.D. candidate the employee. However, the student can apply for funds from a company who can host him/her at its premises (as in the case where Ph.D. students do their research in a company). As another encountered situation, the company and the institute can sign together a funding agreement so that the student still has a public doctoral contract, but is daily located in the company (for example, it is particularly the case of (French) Scientific Cooperation Foundation). Many other resources come from some regional/city projects, some associations, etc.
In India, generally a master's degree is required to gain admission to a doctoral program. Direct admission to a Ph.D. programme after bachelors is also offered by the IITs, the IIITs, the NITs and the Academy of Scientific and Innovative Research. In some subjects, doing a Masters in Philosophy (M.Phil.) is a prerequisite to starting a Ph.D. For funding/fellowship, it is required to qualify for the National Eligibility Test for Lectureship and Junior Research fellowship (NET for LS and JRF)  conducted by the federal research organisation Council of Scientific and Industrial Research (CSIR) and University Grants Commission (UGC).
In the last few years, there have been many changes in the rules relating to a Ph.D. in India . According to the new rules described by UGC, universities must have to conduct entrance exams in general ability and the selected subject. After clearing these tests, the shortlisted candidates need to appear for an interview by the available supervisor/guide. After successful completion of the course work, the students are required to give presentations of the research proposal (plan of work or synopsis) at the beginning, submit progress reports, give a pre-submission presentation and finally defend the thesis in an open defence viva-voce.
In Germany, admission to a doctoral program is generally on the basis of having an advanced degree (i.e., a master's degree, diplom, magister, or staatsexamen), mostly in a related field and having above-average grades. A candidate must also find a tenured professor from a university to serve as the formal advisor and supervisor (Betreuer) of the dissertation throughout the doctoral program called Promotion. This supervisor is informally referred to as Doktorvater or Doktormutter, which literally translate as "doctor's father" or "doctor's mother", respectively. Due to the different college systems in Germany, only professors from universities (Univ.-Prof.) can serve as a doctor's supervisor and therefore, Universities of Applied Sciences (Fachhochschulen) are not entitled to award a doctorate.
Depending on the university, doctoral students (Doktoranden) can be required to attend formal classes or lectures, some of them also including exams or other scientific assignments, in order to get one or more certificates of qualification (Qualifikationsnachweise). Depending on the doctoral regulations (Promotionsordnung) of the university and sometimes on the status of the doctoral student, such certificates may not be required. Usually, former students, research assistants or lecturers from the same university, may be spared from attending extra classes. Instead, under the tutelage of a single professor or advisory committee, they are expected to conduct independent research. In addition to doctoral studies, many doctoral candidates work as teaching assistants, research assistants, or lecturers.
The usual duration of a doctoral program largely depends on the subject and area of research; but, often three to five years of full-time research work are required.
In 2014, the median age of new Ph.D. graduates was 30.4 years of age.
USSR, Russian Federation and former Soviet Republics
The degree of Candidate of Sciences (Russian: кандидат наук, Kandidat Nauk) was the first advanced research qualification in the former USSR (it was introduced there in 1934) and some Eastern Bloc countries (Czechoslovakia, Hungary) and is still awarded in some post-Soviet states (Russian Federation, Ukraine, Belarus and others). According to , in countries with a two-tier system of doctoral degrees (like Russian Federation, some post-Soviet states, Germany, Poland, Austria and Switzerland), should be considered for recognition at the level of the first doctoral degree, and in countries with only one doctoral degree, the degree of Kandidat Nauk should be considered for recognition as equivalent to this Ph.D. degree.
As most education systems only have one advanced research qualification granting doctoral degrees or equivalent qualifications (ISCED 2011, par.270), the degree of Candidate of Sciences (Kandidat Nauk) of the former USSR counties is usually considered at the same level as the doctorate or Ph.D. degrees of those countries.
According to the Joint Statement by the Permanent Conference of the Ministers for Education and Cultural Affairs of the Länder of the Federal Republic of Germany (Kultusministerkonferenz, KMK), German Rectors' Conference (HRK) and the Ministry of General and Professional Education of the Russian Federation, the degree of Kandidat Nauk is recognised in Germany at the level of the German degree of Doktor and the degree of Doktor Nauk at the level of German Habilitation. The Russian degree of Kandidat Nauk is also officially recognised by the Government of the French Republic as equivalent to French doctorate.
In Ukraine, the Supreme Certifying Commission (official English self-denomination, also known as Higher Attestation Commission or "VAK", Ukrainian: Вища атестаційна комісія України), before it was merged into the Ministry of Education and Science, Youth and Sport of the Ukraine, would issue official international diploma supplements to holders of Ukrainian degrees of Kandydat Nauk (Candidate of Sciences, Ukrainian: кандидат наук) stating that the degree was "comparable to the academic degree of Doctor of Philosophy, Ph.D.". In several former Eastern Bloc countries (Czech Republic, Slovakia, Hungary), in which the Candidate of Sciences degrees used to be modeled after the Soviet ones, those degrees have been replaced with Ph.D. or equivalent doctoral degrees, with the recognition of the essential equivalency between the old and the new degrees.
According to the , for purposes of international educational statistics, Kandidat Nauk (Candidate of Sciences) belongs to ISCED level 8, or "doctoral or equivalent", together with Ph.D., D.Phil., D.Litt., D.Sc., LL.D., Doctorate or similar. It is mentioned in the Russian version of ISCED 2011 (par.262) on the UNESCO website as an equivalent to Ph.D. belonging to this level. In the same way as Ph.D. degrees awarded in many English-speaking countries, Kandidat Nauk (Candidate of Sciences) allows its holders to reach the level of the Docent. The second doctorate (or post-doctoral degree) in some post-Soviet states called Doctor of Sciences (Russian: доктор наук, Doktor Nauk) is given as an example of second advanced research qualifications or higher doctorates in ISCED 2011 (par.270) and is similar to Habilitation in Germany, Poland and several other countries. It constitutes a higher qualification compared to Ph.D. as against the or .
About 88% of Russian students studying at state universities study at the expense of budget funds. The average stipend in Russia (as of August 2011) is $430 a year ($35/month). The average tuition fee in graduate school is $2,000 per year.
The Dottorato di ricerca (research doctorate), abbreviated to "Dott. Ric." or "Ph.D.", is an academic title awarded at the end of a course of not less than three years, admission to which is based on entrance examinations and academic rankings in the Bachelor of Arts ("Laurea Triennale") and Master of Arts ("Laurea Magistrale" or "Laurea Specialistica"). While the standard Ph.D. follows the Bologna process, the M.D.-Ph.D. programme may be completed in two years.
The first institution in Italy to create a doctoral program (Ph.D.) was Scuola Normale Superiore di Pisa in 1927 under the historic name "Diploma di Perfezionamento". Further, the research doctorates or Ph.D. (Dottorato di ricerca) in Italy were introduced by law and Presidential Decree in 1980, referring to the reform of academic teaching, training and experimentation in organisation and teaching methods.
Hence, the Superior Graduate Schools in Italy  (Scuola Superiore Universitaria), also called Schools of Excellence (Scuole di Eccellenza) such as Scuola Normale Superiore di Pisa and Sant'Anna School of Advanced Studies still keep their reputed historical "Diploma di Perfezionamento" Ph.D. title by law and MIUR Decree.
Doctorate courses are open, without age or citizenship limits, to all those who already hold a "laurea magistrale" (master degree) or similar academic title awarded abroad which has been recognised as equivalent to an Italian degree by the Committee responsible for the entrance examinations.
The number of places on offer each year and details of the entrance examinations are set out in the examination announcement.
In Federal Democratic Republic of Nepal, generally a master's degree is required to gain admission to a doctoral program. Direct admission to a Ph.D. programme after bachelors is also offered by the NITs, the NITs and the ACSIR. In some subjects, doing a Masters in Philosophy (M.Phil.) is a prerequisite to starting a Ph.D. For funding/fellowship, it is required to qualify for the Nepal Eligibility Test for Lectureship and Junior Research fellowship (NET for LS and JRF)  conducted by the federal research organisation Council of Scientific and Industrial Research (Nepal) (CSIR) and University Grants Commission (UGC). In the last few years, there have been many changes in the rules relating to a Ph.D. in Nepal. According to the new rules, most universities conduct entrance exams in general ability and the selected subject. Apart from Tribhuvan University, many other Universities and private colleges such as South Western State College facilitate scholars to pursue PhD study.
A doctoral degree (Pol. doktor), abbreviated to Ph.D. (Pol. dr) is an advanced academic degree awarded by universities in most fields  as well as by the Polish Academy of Sciences, regulated by the Polish parliament acts and the government orders, in particular by the Ministry of Science and Higher Education of the Republic of Poland. Commonly, students with a master's degree or equivalent are accepted to a doctoral entrance exam. The title of Ph.D. is awarded to a scientist who 1) completed a minimum of 3 years of Ph.D. studies (Pol. studia doktoranckie; not required to obtain Ph.D.), 2) finished his/her theoretical and/or laboratory's scientific work, 3) passed all Ph.D. examinations, 4) submitted his/her dissertation, a document presenting the author's research and findings, 5) successfully defended his/her doctoral thesis. Typically, upon completion, the candidate undergoes an oral examination, always public, by his/her supervisory committee with expertise in the given discipline.
The doctorate was introduced in Sweden in 1477 and in Denmark-Norway in 1479 and awarded in theology, law and medicine, while the magister's degree was the highest degree at the Faculty of Philosophy, equivalent to the doctorate.
Scandinavian countries were among the early adopters of a degree known as a doctorate of philosophy, based upon the German model. Denmark and Norway both introduced the Dr. Phil(os). degree in 1824, replacing the Magister's degree as the highest degree, while Uppsala University of Sweden renamed its Magister's degree Filosofie Doktor (fil. dr) in 1863. These degrees, however, became comparable to the German Habilitation rather than the doctorate, as Scandinavian countries did not have a separate Habilitation. The degrees were uncommon and not a prerequisite for employment as a professor; rather, they were seen as distinctions similar to the British (higher) doctorates (D.Litt., D.Sc.). Denmark introduced an American-style Ph.D. in 1989; it formally replaced the Licentiate's degree, and is considered a lower degree than the dr. phil. degree; officially, the ph.d. is not considered a doctorate, but unofficially, it is referred to as "the smaller doctorate", as opposed to the dr. phil., "the grand doctorate". Holders of a ph.d. degree are not entitled to style themselves as "Dr." Currently Denmark distinctions between the dr. phil. as the proper doctorate and a higher degree than the ph.d., whereas in Norway, the historically analogous dr. philos. degree is officially regarded as equivalent to the new ph.d.
In Sweden, the doctorate of philosophy was introduced at Uppsala University's Faculty of Philosophy in 1863. In Sweden, the Latin term is officially translated into Swedish filosofie doktor and commonly abbreviated fil. dr or FD. The degree represents the traditional Faculty of Philosophy and encompasses subjects from biology, physics and chemistry, to languages, history and social sciences, being the highest degree in these disciplines. Sweden currently has two research-level degrees, the Licentiate's degree, which is comparable to the Danish degree formerly known as the Licentiate's degree and now as the ph.d., and the higher doctorate of philosophy, Filosofie Doktor. Some universities in Sweden also use the term teknologie doktor for doctorates awarded by institutes of technology (for doctorates in engineering or natural science related subjects such as materials science, molecular biology, computer science etc.). The Swedish term fil. dr is often also used as a translation of corresponding degrees from e.g. Denmark and Norway.
Doctoral degrees are regulated by Real Decreto (Royal Decree in Spanish) R.D. 1393/2007, and will be regulated R.D. 99/2011, starting with the 2014/2015 academic year. They are granted by a university on behalf of the King, and its diploma has the force of a public document. The Ministry of Science keeps a National Registry of Theses called TESEO.
All doctoral programs are of a research nature. A minimum of three years of study are required, in one only stage:
- A 3-year (or longer) period of research. Extensions may be requested for maximum 5 years. The student must write his thesis presenting a new discovery or original contribution to science. If approved by her or his "thesis director (or directors)", the study will be presented to a panel of 5 distinguished scholars. Any doctor attending the public presentations is allowed to challenge the candidate with questions on his research. If approved, he will receive the doctorate. Four marks can be granted: Unsatisfactory, Pass, Satisfactory, and Excellent. "Cum laude" (with all honours, in Latin) denomination can be added to the Excellent ones if all five members of the tribunal agree.
A doctoral degree is required to apply to a long-term teaching position at a university.
The social standing of doctors in Spain is evidenced by the fact that only Ph.D. holders, Grandees and Dukes can take seat and cover their heads in the presence of the King. All Doctor Degree holders are reciprocally recognized as equivalent in Germany and Spain ("Bonn Agreement of November 14, 1994").
Universities admit applicants to Ph.D. programmes on a case-by-case basis; depending on the university, admission is typically conditional on the prospective student having successfully completed an undergraduate degree with at least upper second-class honours, or a postgraduate master's degree, but requirements can vary.
In the case of the University of Oxford, for example, "The one essential condition of being accepted ... is evidence of previous academic excellence, and of future potential." The University of Oxford (and the University of Sussex) also abbreviates their Doctor of Philosophy degree as D.Phil. but in other respects is equivalent to a PhD. Commonly, students are first accepted on to an MPhil programme and may transfer to Ph.D. regulations upon satisfactory progress and is referred to as APG (Advanced Postgraduate) status. This is typically done after one or two years, and the research work done may count towards the PhD degree. If a student fails to make satisfactory progress, he or she may be offered the opportunity to write up and submit for an MPhil degree as is the case at the King's College London and University of Manchester. In contrast, in other universities such as the University of Cambridge and University College London the MPhil is offered as a taught or stand-alone research degree.
In addition, Ph.D. students from countries outside the EU/EFTA area are required to comply with the Academic Technology Approval Scheme (ATAS), which involves undergoing a security clearance process with the Foreign Office for certain courses in medicine, mathematics, engineering and material sciences. This requirement was introduced in 2007 due to concerns about terrorism and weapons proliferation.
In the United Kingdom, funding for Ph.D. students is sometimes provided by government-funded Research Councils or the European Social Fund, usually in the form of a tax-free bursary which consists of tuition fees together with a stipend of around £13,000 per year for three years (higher in London), whether or not the degree continues for longer. Scientific studentships are usually paid at a higher rate, for example, in London, Cancer Research UK, the ICR and the Wellcome Trust stipend rates start at around £19,000 and progress annually to around £23,000 a year; an amount that is tax and national insurance free. Research Council funding is sometimes 'earmarked' for a particular department or research group, who then allocate it to a chosen student, although in doing so they are generally expected to abide by the usual minimum entry requirements (typically a first degree with upper second class honours, although successful completion of a postgraduate master's degree is usually counted as raising the class of the first degree by one division for these purposes). However, the availability of funding in many disciplines (especially humanities, social studies, and pure science subjects) means that in practice only those with the best research proposals, references and backgrounds are likely to be awarded a studentship. The ESRC (Economic and Social Science Research Council) explicitly state that a 2.1 minimum (or 2.2 plus additional master's degree) is required—no additional marks are given for students with a first class honours or a distinction at masters level. Since 2002, there has been a move by research councils to fund interdisciplinary doctoral training centres which concentrate resources on fewer higher quality centres.
Many students who are not in receipt of external funding may choose to undertake the degree part-time, thus reducing the tuition fees, as well as creating free time in which to earn money for subsistence. Students may also take part in tutoring, work as research assistants, or (occasionally) deliver lectures, at a rate of typically £25–30 per hour, either to supplement existing low income or as a sole means of funding.
There is usually a preliminary assessment to remain in the programme and the thesis is submitted at the end of a three- to four-year programme. These periods are usually extended pro rata for part-time students. With special dispensation, the final date for the thesis can be extended for up to four additional years, for a total of seven, but this is rare. For full-time Ph.D.s, a 4-year time limit has now been fixed and students must apply for an extension to submit a thesis past this point. Since the early 1990s, British funding councils have adopted a policy of penalising departments where large proportions of students fail to submit their theses in four years after achieving Ph.D.-student status (or pro rata equivalent) by reducing the number of funded places in subsequent years.
There has recently been an increase in the number of Integrated Ph.D. programs available, such as at the University of Southampton. These courses include a Master of Research (MRes) in the first year, which consists of a taught component as well as laboratory rotation projects. The Ph.D. must then be completed within the next 3 years. As this includes the MRes all deadlines and timeframes are brought forward to encourage completion of both MRes and Ph.D. within 4 years from commencement. These programmes are designed to provide students with a greater range of skills than a standard Ph.D.; and for the university they are a means of gaining an extra years' fees from public sources.
In the United Kingdom Ph.D. degrees are distinct from other doctorates, most notably the higher doctorates such as D.Litt. (Doctor of Letters) or D.Sc. (Doctor of Science), which may be granted on the recommendation of a committee of examiners on the basis of a substantial portfolio of submitted (and usually published) research. However, some UK universities still maintain the option of submitting a thesis for the award of a higher doctorate.
Recent years have seen the introduction of professional doctorates (D.Prof or ProfD), which are the same level as Ph.D.'s but more specific in their field. These tend not to be solely academic, but combine academic research, a taught component and a professional qualification. These are most notably in the fields of engineering (Eng.D.), education (Ed.D.), educational psychology (D.Ed.Psych), occupational psychology (D.Occ Psych.) clinical psychology (D.Clin.Psych.), social work (DSW), nursing (DNP), public administration (DPA), business administration (DBA), and music (DMA). These typically have a more formal taught component consisting of smaller research projects, as well as a 40,000–60,000 word thesis component, which together are officially considered equivalent to a Ph.D. degree.
In the United States, the Ph.D. degree is the highest academic degree awarded by universities in most fields of study. U.S. students typically undergo a series of three phases in the course of their work toward the Ph.D. degree. The first phase consists of coursework in the student's field of study and requires one to three years to complete. This often is followed by a preliminary, a comprehensive examination, or a series of cumulative examinations where the emphasis is on breadth rather than depth of knowledge. The student is often later required to pass oral and written examinations in the field of specialization within the discipline, and here, depth is emphasized. Some Ph.D. programs require the candidate to successfully complete requirements in pedagogy (taking courses on higher level teaching and teaching undergraduate courses) or applied science (e.g., clinical practice and predoctoral clinical internship in Ph.D. programs in clinical, counseling, or school psychology).
Another two to eight years are usually required for the composition of a substantial and original contribution to human knowledge in the form of a written dissertation, which in the social sciences and humanities typically ranges from 50 to 450 pages. In many cases, depending on the discipline, a dissertation consists of a comprehensive literature review, an outline of methodology, and several chapters of scientific, social, historical, philosophical, or literary analysis. Typically, upon completion, the candidate undergoes an oral examination, sometimes public, by his or her supervisory committee with expertise in the given discipline.
There are 282 universities in the United States that award the Ph.D. degree, and those universities vary widely in their criteria for admission, as well as the rigor of their academic programs. Typically, Ph.D. programs require applicants to have a bachelor's degree in a relevant field (and, in many cases in the humanities, a master's degree), reasonably high grades, several letters of recommendation, relevant academic coursework, a cogent statement of interest in the field of study, and satisfactory performance on a graduate-level exam specified by the respective program (e.g., GRE, GMAT). The number of Ph.D. diplomas awarded by US universities has risen nearly every year since 1957, according to data compiled by the US National Science Foundation. In 1957, US universities awarded 8,611 Ph.D. diplomas; 20,403 in 1967; 31,716 in 1977; 32,365 in 1987; 42,538 in 1997; and 48,133 in 2007.
Depending on the specific field of study, completion of a Ph.D. program usually takes four to eight years of study after the Bachelor's Degree; those students who begin a Ph.D. program with a master's degree may complete their Ph.D. degree a year or two sooner. As Ph.D. programs typically lack the formal structure of undergraduate education, there are significant individual differences in the time taken to complete the degree. Overall, 57% of students who begin a Ph.D. program in the US will complete their degree within ten years, approximately 30% will drop out or be dismissed, and the remaining 13% of students will continue on past ten years.
Ph.D. students at U.S. universities typically receive a tuition waiver and some form of annual stipend. Many U.S. Ph.D. students work as teaching assistants or research assistants. Graduate schools increasingly encourage their students to seek outside funding; many are supported by fellowships they obtain for themselves or by their advisers' research grants from government agencies such as the National Science Foundation and the National Institutes of Health. Many Ivy League and other well-endowed universities provide funding for the entire duration of the degree program (if it is short) or for most of it.
Models of supervision
At some universities, there may be training for those wishing to supervise Ph.D. studies. There is now a lot of literature published for academics who wish to do this, such as Delamont, Atkinson and Parry (1997). Indeed, Dinham and Scott (2001) have argued that the worldwide growth in research students has been matched by increase in a number of what they term "how-to" texts for both students and supervisors, citing examples such as Pugh and Phillips (1987). These authors report empirical data on the benefits that a Ph.D. candidate may gain if he or she publishes work, and note that Ph.D. students are more likely to do this with adequate encouragement from their supervisors.
Wisker (2005) has noticed how research into this field has distinguished between two models of supervision: The technical-rationality model of supervision, emphasising technique; The negotiated order model, being less mechanistic and emphasising fluid and dynamic change in the Ph.D. process. These two models were first distinguished by Acker, Hill and Black (1994; cited in Wisker, 2005). Considerable literature exists on the expectations that supervisors may have of their students (Phillips & Pugh, 1987) and the expectations that students may have of their supervisors (Phillips & Pugh, 1987; Wilkinson, 2005) in the course of Ph.D. supervision. Similar expectations are implied by the Quality Assurance Agency's Code for Supervision (Quality Assurance Agency, 1999; cited in Wilkinson, 2005).
International PhD equivalent degrees
- Afghanistan: ډاکټر
- Albania: Doktorature (Dr.)
- Algeria: Doctorat, دكتوراه
- Argentina: Doctorado (Dr.)
- Armenia: գիտությունների թեկնածու, դոցենտ
- Austria: Doktor (Dr., plural: DDr.)
- Azerbaijan: Doktorantura (Dr.)
- Bangladesh: Doctorate
- Belarus: кандидат наук
- Belgium (Dutch-speaking): Doctor
- Belgium (French-speaking): Doctorat
- Bosnia and Herzegovina: Doktor
- Brazil: Doutorado
- Bulgaria: Доктор
- Burma: ပါရဂူဘြဲ႕
- China: 博士 (Bo-shi)
- Chile: Doctorado
- Colombia: Doctorado
- Costa Rica: Ph.D. or Doctorado (Dr.)
- Croatia: Doktor
- Czech Republic: CSc. and DrSc. was used till 1998, since 1998 Ph.D. written as Ph.D. is used
- Denmark: Licentiate, Magister, Ph.D. (the doctorates are higher degrees)
- Dominican Republic: Doctorado
- Ecuador: Doctorado
- El Salvador: Doctorado
- Egypt: Doctorat, دكتوراه
- Estonia: Doktor
- Ethiopia: ዶክተር, Doctor (Ph.D., Dr.)
- Finland: Filosofian tohtori and any degree of tohtori
- France: Doctorat
- Germany: Doktor
- Greece: Διδακτορικό
- Hong Kong: 博士 (Doctor)
- India: Doctorate
- Indonesia: Doktor
- Iran: دکترا (Doctora)
- Iraq: دكتوراه (Duktorah)
- Ireland: an Doctúireacht
- Israel: דוקטורט ("doctorat")
- Italy: Dottorato di ricerca
- Japan: 博士 (hakase)
- Jordan: دكتوراه (Doctorah)
- Korea: 박사 (baksa)
- Kuwait: دكتوراه (Dektoraah)
- Latin America: Doctorado/Doctorate
- Latvia: Zinātņu doktors
- Lebanon: دكتوراه (doktorah)
- Lithuania: Daktaras
- Macau: 博士 (Doutoramento)
- Macedonia: Докторат
- Malaysia: Doktor Falsafah
- Mexico: Doctorado
- Mongolia: Эрдэмтэн
- Morocco: Doctorat
- Netherlands: Doctor
- Nigeria: Doctor of Philosophy (Ph.D.)
- Norway: Magister, Licentiate, doctorates (traditionally considered higher degrees), Ph.D.
- Pakistan: Doctor
- Paraguay: Ph.D. or Doctorado (Dr.)
- Peru: Doctorado
- Philippines: Doktor
- Poland: Doktor
- Portugal: pt:Doutoramento
- Romania: Doctorat
- Russia: ru: кандидат наук (PhD junior grade), ru: доктор наук (PhD senior grade)
- Saudi Arabia دكتوراه
- Singapore: Doctor
- Serbia: Доктор
- Slovakia: CSc. was used during communism and some years in 90s, now Ph.D. written as Ph.D. is used; DrSc. is a higher degree.
- Slovenia: Doktor
- Spain: Doctorado
- Sweden: Filosofie doktor (fil.dr., FD)
- Switzerland: Doctorat (Dr)
- Syria: دكتوراه (doktorah)
- Taiwan： 博士
- Thailand: ดุษฎีบัณฑิต
- Tunisia: دكتوراه (doktorah)
- Turkey: Doktora
- United Arab Emirates: ar:دكتوراه (doktorah)
- United Kingdom: Doctor of Philosophy (PhD, doctor, the abbreviation DPhil is used only by the University of Oxford and the University of Sussex)
- United States: Doctor of Philosophy (PhD)
- Ukraine: uk: кандидат наук (CSc.)
- Uruguay: Doctorado
- Uzbekistan: Fan nomzodi (CSc.)
- Venezuela: Doctorado
- Vietnam: Tiến sĩ
- Candidate of Philosophy (also "All But Dissertation", ABD): a term, usually used unofficially, for a graduate student who has completed all Ph.D. coursework but has yet to defend his or her dissertation
- History of higher education in the United States#Graduate schools
- List of fields of doctoral studies in the United States
- Ph.D. in management, a program designed for students interested in becoming university professors in the field of business
- Piled Higher and Deeper, Life (or the lack thereof) in Academia, a comic strip by Jorge Cham
- Terminal degree, the highest degree awarded in a field, usually a Ph.D.