Doctoral Dissertation Requirements

PhD Degree Requirements

The only doctoral degree offered by The Graduate School (TGS) is the doctor of philosophy (PhD) degree. In some cases, this degree is offered in conjunction with another degree, whether from another program administered by TGS or from another school at Northwestern University.

The Doctor of Philosophy degree is oriented toward research that will advance knowledge. Study for a specified time and accumulation of credit toward residency for courses taken are not by themselves sufficient to earn the PhD degree. A student must demonstrate scholarly distinction and the ability to advance knowledge through independent research by achieving admission to candidacy and writing a dissertation.

Each student enrolled in a PhD program must have a principal research advisor and a committee.

The principal research advisor (also known as mentor, PI, dissertation director, advisor) is a member of the Northwestern University Graduate Faculty who works with the student to develop a research topic, formulate ideas and structure for, and guides the progress of the thesis/prospectus/dissertation. In some cases, although rare, there is a Principal Research Co-Advisor who also works with the student to develop a research topic, formulate ideas and structure for, and guides the progress of the thesis/prospectus/dissertation.

The committee members are those who have expertise in and inform the student's area of research, serve as a reader of the thesis, prospectus, or dissertation, and vote on the outcome of the proposal defense/final exam. The committee chair is a member of the Graduate Faculty who leads the committee for the defense of the prospectus or final exam (dissertation). In some cases, there is a Committee Co-Chair who co-leads the committee. The Committee Chair may or may not be the same individual as the Principal Research Advisor. A minimum of three individuals must serve on the final exam committee. At least two members of this committee, including the chair, must be members of the Northwestern University Graduate Faculty.

All Northwestern University graduate students, must fulfill a set of requirements regarding

12.1 PhD Coursework and Registration

A student who enters a doctoral program must successfully complete at least nine letter-graded courses (non P/NP) authorized for graduate credit. A 3.0 cumulative GPA must be maintained. TGS does not accept transfer credit in lieu of the 9 letter-graded minimum course requirement.

Two types of advanced courses, 499 Independent Study (or 499 Projects) and 590 Research, are applicable to residency credit but bear restrictions concerning either when they may be taken during a student's academic career or total allowable credits:

  • 499 Independent Study - For doctoral students, independent studies may not represent more than half of the total units taken in the first three quarters of enrollment in a PhD program.
  • Program courses identified as 590 Research, may be taken for one, two, three, or four course units per quarter. Generally, this registration is not available to students until a core of basic courses has been completed. All 590 Research registrations must be taken on a P/N/K basis

Students in quarter nine and beyond may have additional course requirements to complete in their program and may register for up to four units:

  • Students who are funded and who register for less than three units must also register for TGS 500. All course requirements for a doctoral program must be completed by the end of the twelfth quarter.
  • Students in quarters thirteen and above may register for non-required coursework in addition to TGS 500 if the courses are related to the student's area of study.
  • Grading for advanced year registrations must adhere to existing grading policies.

12.2 PhD Residency

Residency is calculated in terms of quarters of full-time study. A student pursuing a doctoral degree must complete eight quarters of residency consecutively over two years, including summers (see the PhD Timeline Completion). Approved leaves of absence or parental accommodation may alter the residency timeline.

No PhD residency credit will be awarded by The Graduate School (TGS) for work completed in a graduate program prior to admission to and enrollment in the PhD program in TGS. Individual programs may waive course requirements based on work completed at another institution (either prior to or after enrollment at Northwestern), but all doctoral students must complete nine letter-graded (A,B,C) courses authorized by TGS for graduate credit, eight quarters of residency, and maintain a 3.0 GPA. Students may register for 590 Research within their programs to maintain full-time registration during quarters in which they are not enrolled full-time in graded coursework.

12.3 PhD Candidacy

Admission to The Graduate School (TGS) does not constitute or guarantee a student's admission to candidacy for the PhD degree. Admission to candidacy is contingent upon the recommendation of the student's department or program and upon approval of The Graduate School.

A student must be admitted to candidacy by the end of the third year of study, which falls on the last date of the 12th quarter. A student failing to meet this milestone will be considered not in good academic standing and therefore will be placed on academic probation. Deadlines will be altered in the case of an approved leave of absence or parental accommodation.

  • Admission to candidacy is reached by passing a comprehensive qualifying examination, written or oral or both. Individual departments or programs determine the character of this examination. At the time of admission to candidacy, proficiency in the major and related fields is certified and additional requirements for the PhD degree are stipulated. Students should be aware of requirements for admission to candidacy established by both the department or program and the Graduate Faculty.
  • The Director of Graduate Studies (or DGS designate) submits the PhD Qualifying Exam form online via TGS Forms in CAESAR (SES). The program must submit approval of this form before the end of a student's third year. Following the submission of the approved Qualifying Exam form in SES students are admitted to candidacy. Students are notified via email by TGS of approval of their Qualifying exam form and admission to candidacy.

12.4 PhD Prospectus

Students must have a prospectus (dissertation proposal) approved by their committee no later than the end of the fourth year of study, which falls on the last date of the 16th quarter. A student failing to meet this milestone will be considered not in good academic standing and therefore will be placed on academic probation. Deadlines will be altered in the case of an approved leave of absence or parental accommodation. The prospectus must be approved by a faculty committee. A minimum of three individuals must serve on the prospectus committee. At least two members of this committee, including the chair, must be members of the Northwestern University Graduate Faculty. The student must submit the PhD Prospectus form through TGS Forms in CAESAR. The program must approve this form online before TGS enters the final approval. Students are notified via email by TGS of approval of their prospectus form.

12.5 PhD Dissertation

Every candidate for the PhD degree must present a dissertation that gives evidence of original and significant research.

12.5.1 Dissertation Assistance

All dissertators should consult with their advisors about appropriate forms of assistance before assistance is rendered. Dissertations must acknowledge assistance received in any of the following areas:

  • Designing the research
  • Executing the research
  • Analyzing the data
  • Interpreting the data/research
  • Writing, proofing, or copyediting the manuscript 

12.5.2 Formatting

Dissertations must be formatted according to the Dissertation Formatting Guidelines document. Dissertations not conforming to these instructions will not be accepted by The Graduate School.

12.5.3 Depositing the Dissertation

Dissertations must be deposited into the ProQuest Database. In addition, the University Library receives a copy of the dissertation that may be used at its discretion for reasons including but not limited to long term archiving, library use and interlibrary loan, and dissemination through an institutional repository or other means. The library also archives electronic copies of dissertations to help ensure that the content is preserved for future generations. 

12.5.4 Dissertation Embargo

A student wishing to delay public release of their dissertation for an initial embargo of up to two years must submit a request providing a clearly stated rationale. Whatever the rationale, the student should be sure to consult with their faculty mentor(s) before considering an embargo, since support of a faculty member well versed with the student’s work and the fields it engages – presumably the primary advisor – is required for the request to be reviewed by TGS Academic Affairs, which will consult with all parties concerned before making a final determination as to whether the dissertation can be embargoed. 

An approved request to place an embargo has the effect of restricting online access to the dissertation through the library's discovery systems and ProQuest for the period of the embargo. Metadata (author,
title, abstract, keywords and subjects) about the embargoed dissertation will be available through the ProQuest system and the library catalog. Users of those systems are able to search for and see the metadata, but not the actual text or other content of the dissertation.

The dissertation will automatically be released in the library's discovery systems and ProQuest after the approved embargo expires. To extend the embargo with ProQuest, students should contact ProQuest Support directly. To extend the embargo with the University Library, students must contact TGS at least thirty days prior to the point of expiration. The student may request a one-time extension of the embargo for up to six years and must provide a sufficient intellectual and/or professional rationale in seeking approval from TGS Academic Affairs.

12.6 PhD Completion

Scheduling the final examination (dissertation defense) is the responsibility of the candidate and the members of the committee.

  • The PhD final exam must be approved by a faculty committee. A minimum of three individuals must serve on the final exam committee. At least two members of this committee, including the chair, must be members of the Northwestern University Graduate Faculty.

12.6.1 Filing Requirements and Forms

Students pursuing the Doctor of Philosophy degree must file the following required documents prior to graduation and by the published deadlines:

  • Application for Degree: this form must be filled out via CAESAR. Students should login to CAESAR, click on "Main Menu"-> "TGS Forms" and navigate to "Application for a Degree" form.
  • PhD Final Exam Form: this form must be filled out via CAESAR. Students should login to CAESAR, click on "Main Menu" -> "TGS Forms" and navigate to "TGS PhD Final Exam" form. Students must print out a hard copy of the completed form to take to the PhD final exam. Each committee member must sign the form. The signed form should go to the Director of Graduate Studies (or their designate) who will finish the approval process online; the form will be submitted to The Graduate School electronically for final approval, with the signed copy to follow.
  • Dissertation submission via ProQuest's website. Once the dissertation has been approved by the committee and all edits and revisions are complete, the student must submit online via ProQuest. The dissertation must conform to TGS formatting standards on the Dissertation Formatting Guidelines document. Once the student has submitted the dissertation online, a Student Services representative will review its formatting and confirm via email that the dissertation is acceptable or notify the student if changes need to be made.

Change of Grade forms: Students with Y or K grades on their transcript must work with their program/department to ensure the appropriate change of grade forms are submitted to The Graduate School by the published deadline.

12.7 PhD Timeline

The Graduate School policy states that all requirements for the doctoral degree must be met within nine years of initial registration in a doctoral program, which falls on the last day of the 36th quarter. For students on an approved leave of absence or approved parental accommodation, milestones will be extended accordingly.

Year OneTuition RateRegistrationMilestones to be AchievedForms to be Completed
Q1 - FallFull Rate3-4 units of coursework or 590Coursework towards residency requirement. A minimum of nine letter-graded (ABC) courses approved by TGS for graduate credit are required. Individual programs may require more graded courses.
Q2 - Winter3-4 units of coursework or 590
Q3 - Spring3-4 units of coursework or 590
Q4 - Summer3-4 units of coursework or 590
Year TwoTuition RateRegistrationMilestones to be AchievedForms to be Completed
Q5 - FallFull Rate3-4 units of coursework or 590Coursework towards residency requirement. A minimum of nine letter-graded (ABC) courses approved by TGS for graduate credit are required. Individual programs may require more graded courses
Q6 - Winter3-4 units of coursework or 590
Q7 - Spring3-4 units of coursework or 590
Q8 - Summer3-4 units of coursework or 590
Year ThreeTuition RateRegistrationMilestones to be AchievedForms to be Completed
Q9 - FallAdvanced RateTGS 500 and/or courseworkCoursework towards program requirements (if applicable). Students must complete all required courses (including incomplete grades/F grade make-up) and be admitted to candidacy (PhD Qualifying Exam) by the end of the twelfth quarter. Students who have completed their program requirements will register for TGS 500 in addition to any non-required (extra) coursework. Students who have not completed their program requirements will register for courses as determined by their program.PhD Qualifying Exam form (submitted by program. No student entry)
Q10 - WinterTGS 500 and/or coursework
Q11 - SpringTGS 500 and/or coursework
Q12 - SummerTGS 500 and/or coursework
Year FourTuition RateRegistrationMilestones to be AchievedForms to be Completed
Q13 - FallAdvanced RateTGS 500 in addition to non-required courseworkStudents must complete their prospectus (proposal of dissertation topic) before the end of the sixteenth quarter.PhD Prospectus form (submitted by student via TGS Forms in CAESAR ; approved online by program)
Q14 - Winter
Q15 - Spring
Q16 - Summer
Year FiveTuition RateRegistrationMilestones to be AchievedForms to be Completed
Q17 - FallAdvanced RateTGS 500 in addition to non-required courseworkStudents who are completing their degree must complete: (1) Application for Degree via TGS Forms in CAESAR; (2) PhD Final Exam Form via TGS Forms in CAESAR to be approved by the program (3) Online submission of dissertation via ProQuest
Q18 - Winter
Q19 - Spring
Q20 - Summer
Year SixTuition RateRegistrationMilestones to be AchievedForms to be Completed
FallAdvanced Rate or Continuous RegistrationTGS 500 if receiving funding; TGS 512 if unfundedDegree deadline - students have 9 years from matriculation to complete the PhD degree. Only rarely under extenuating circumstances will students be granted permission to continue beyond 9 years.Students who are completing their degree will complete the following forms: (1) Application for Degree via TGS Forms in CAESAR; (2) PhD Final Exam Form via TGS Forms in CAESAR which will be approved by the program (3) Online submission of dissertation via UMI ProQuest.
Winter
Spring
Summer
PhD students who do not complete their PhD program within  9 years of initial registration in the doctoral program will be placed on academic probation.

What is a Ph.D. Dissertation?

[I wrote this in 1993 as a letter to a student concerning a draft of his dissertation. in 2003 I edited it to remove some specific references to the student and present it as a small increment to the information available to my grad students. --spaf]


Let me start by reviewing some things that may seem obvious:

  1. Your dissertation is part of the requirements for a PhD. The research, theory, experimentation, et al. also contribute. One does not attempt to capture everything in one's dissertation.
  2. The dissertation is a technical work used to document and set forth proof of one's thesis. It is intended for a technical audience, and it must be clear and complete, but not necessarily exhaustively comprehensive. Also note -- experimental data, if used, is not the proof -- it is evidence. The proof is presented as analysis and critical presentation. As a general rule, every statement in your dissertation must be common knowledge, supported by citation to technical literature, or else original results proved by the candidate (you). Each of those statements must directly relate to the proof of the thesis or else they are not needed.
  3. The dissertation is not the thesis. One's thesis is a claim -- a hypothesis. The dissertation describes, in detail, how one proves the hypothesis (or, rarely, disproves the claim and shows other important results).

Let's revisit the idea of the thesis itself. It is a hypothesis, a conjecture, a theorem. The dissertation is a formal, stylized document used to argue your thesis. The thesis must be significant, original (no one has yet demonstrated it to be true), and it must extend the state of scientific knowledge.

The first thing you need to do is to come up with no more than three sentences that express your thesis. Your committee must agree that your statements form a valid thesis statement. You too must be happy with the statement -- it should be what you will tell anyone if they ask you what your thesis is (few people will want to hear an hour presentation as a response).

Once you have a statement of thesis, you can begin to develop the dissertation. The abstract, for instance, should be a one-page description of your thesis and how you present the proof of it. The abstract should summarize the results of the thesis and should stress the contributions to science made thereby.

Perhaps the best way to understand how an abstract should look would be to examine the abstracts of several dozen dissertations that have already been accepted. Our university library has a collection of them. This is a good approach to see how an entire dissertation is structured and presented. MIT press has published the ACM doctoral dissertation award series for over a decade, so you may find some of those to be good examples to read -- they should be in any large technical library.

The dissertation itself should be structured into 4 to 6 chapters. The following is one commonly-used structure:

  1. Introduction. Cover an introduction to the basic terminology, give citations to appropriate background work, briefly discuss related work that has already covered aspects of the problem.
  2. Abstract model. Discuss an abstract model of what you are trying to prove. This chapter should not discuss any specific implementation (see below)
  3. Validation of model/proof of theorems. This is a chapter showing a proof of the model. This could be a set of proofs, or a discussion of construction and validation of a model or simulation to be used in gathering supporting data.
  4. Measurements/data. This would be a presentation of various data collected from real use, from simulations, or from other sources. The presentation would include analysis to show support for the underlying thesis.
  5. Additional results. In some work there may be secondary confirmation studies, or it might be the case that additional important results are collected along the way to the proof of the central thesis. These would be presented here.
  6. Conclusions and future work. This is where the results are all tied together and presented. Limitations, restrictions and special cases should be clearly stated here along with the results. Some clear extensions to future work may also be described.

Let's look at these in a little more detail

Chapter I, Introduction. Here, you should clearly state the thesis and its importance. This is also where you give definitions of terms and other concepts used elsewhere. There is no need to write 80 pages of background on your topic here. Instead, you can cover almost everything by saying: "The terminology used in this work matches the definitions given in [citation, citation] unless noted otherwise." Then, cite some appropriate works that give the definitions you need. The progress of science is that we learn and use the work of others (with appropriate credit). Assume you have a technically literate readership familiar with (or able to find) common references. Do not reference popular literature or WWW sites if you can help it (this is a matter of style more than anything else -- you want to reference articles in refereed conferences and journals, if possible, or in other theses).

Also in the introduction, you want to survey any related work that attempted something similar to your own, or that has a significant supporting role in your research. This should refer only to published references. You cite the work in the references, not the researchers themselves. E.g., "The experiments described in [citation] explored the foo and bar conditions, but did not discuss the further problem of baz, the central point of this work." You should not make references such as this: "Curly, Moe and Larry all believed the same in their research [CML53]" because you do not know what they actually believed or thought -- you only know what the paper states. Every factual statement you make must have a specific citation tied to it in this chapter, or else it must be common knowledge (don't rely on this too much).

Chapter II. Abstract Model. Your results are to be of lasting value. Thus, the model you develop and write about (and indeed, that you defend) should be one that has lasting value. Thus, you should discuss a model that is not based on Windows, Linux, Ethernet, PCMIA, or any other specific technology. It should be generic in nature, and should capture all the details necessary to overlay the model on likely environments. You should discuss the problems, parameters, requirements, necessary and sufficient conditions, and other factors here. Consider that 20 years ago (ca 1980) the common platform was a Vax computer running VMS or a PDP-11 running Unix version 6, yet well-crafted theses of the time are still valuable today. Will your dissertation be valuable 20 years from now (ca 2020), or have you referred to technologies that will be of only historical interest?

This model is tough to construct, but is really the heart of the scientific part of your work. This is the lasting part of the contribution, and this is what someone might cite 50 years from now when we are all using MS Linux XXXXP on computers embedded in our wrists with subspace network links!

Chapters III & IV, Proof. There are basically three proof techniques that I have seen used in a computing dissertation, depending on the thesis topic. The first is analytic, where one takes the model or formulae and shows, using formal manipulations, that the model is sound and complete. A second proof method is stochastic, using some form of statistical methods and measurements to show that something is true in the anticipated cases.

Using the third method, you need to show that your thesis is true by building something according to your model and showing that it behaves as you claim it will. This involves clearly showing how your implementation model matches the conditions of your abstract model, describing all the variables and why you set them as you do, accounting for confounding factors, and showing the results. You must be careful to not expend too much effort describing how standard protocols and hardware work (use citations to the literature, instead). You must clearly express the mapping of model to experiment, and the definition of parameters used and measured.

Chapter V. Additional results. This may be folded into Chapter III in some theses, or it may be multiple chapters in a thesis with many parts (as in a theory-based thesis). This may be where you discuss the effects of technology change on your results. This is also a place where you may wish to point out significant results that you obtained while seeking to prove your central thesis, but which are not themselves supportive of the thesis. Often, such additional results are published in a separate paper.

Chapter VI. Conclusions and Future work. This is where you discuss what you found from your work, incidental ideas and results that were not central to your thesis but of value nonetheless, (if you did not have them in Chapter V) and other results. This chapter should summarize all the important results of the dissertation --- note that this is the only chapter many people will ever read, so it should convey all the important results.

This is also where you should outline some possible future work that can be done in the area. What are some open problems? What are some new problems? What are some significant variations open to future inquiry?

Appendices. Appendices usually are present to hold mundane details that are not published elsewhere, but which are critical to the development of your dissertation. This includes tables of measurement results, configuration details of experimental testbeds, limited source code listings of critical routines or algorithms, etc. It is not appropriate to include lists of readings by topic, lists of commercial systems, or other material that does not directly support the proof of your thesis.

Here are some more general hints to keep in mind as you write/edit:

  • Adverbs should generally not be used -- instead, use something precise. For example, do not say that something "happens quickly." How fast is quickly? Is it relative to CPU speeds? Network speeds? Does it depend on connectivity, configuration, programming language, OS release, etc? What is the standard deviation?
  • As per the above, use of the words "fast", "slow", "perfect", "soon", "ideal", "lots of" and related should all be avoided. So should "clearly", "obviously", "simple", "like", "few", "most", "large", et al.
  • What you are writing is scientific fact. Judgments of aesthetics, ethics, personal preference, and the like should be in the conclusions chapter if they should be anywhere at all. With that in mind, avoid use of words such as "good", "bad", "best", and any similar discussion. Also avoid stating "In fact," "Actually," "In reality," and any similar construct -- everything you are writing must be factual, so there is no need to state such things. If you feel compelled to use one of these constructs, then carefully evaluate what you are saying to be certain you are not injecting relative terms, opinions, value judgements, or other items that are inappropriate for a dissertation.
  • Computers and networks do not have knees, so poor performance cannot bring them to something they do not have. They also don't have hands, so "On the one hand..." is not good usage. Programs don't perform conscious thought (nor do their underlying computers), so your system does not "think" that it has seen a particular type of traffic. Generalizing from this, do not anthropomorphize your IT components!
  • Avoid mention of time and environment. "Today's computers" are antiques far sooner than you think. Your thesis should still be true many years from now. If a particular time or interval is important, then be explicit about it, as in "Between 1905 and 1920" rather than "Over the last 15 years." (See the difference, given some distance in time?)
  • Be sure that something you claim as a proof would be recognized as such by any scientist or mathematician.
  • You and your dissertation are supposed to be the ultimate (current) authority on the topic you are covering. Thus, there should be no instance of "to the best of our knowledge" or "as far as we can tell." Either you know for certain, or you don't -- and if you don't know, you shouldn't state it!
  • Focus on the results and not the methodology. Methodology should be clearly described, but not the central topic of your discussion in chapters III & IV
  • Keep concepts and instances separate. An algorithm is not the same as a program that implements it. A protocol is not the same as the realization of it, a reference model is not the same as a working example, and so on.

As a rule of thumb, a CS dissertation should probably be longer than 100 pages, but less than 160. Anything outside of that range should be carefully examined with the above points in mind.

Keep in mind that you -- the Ph.D. candidate -- are expected to become the world's foremost expert on your topic area. That topic area should not be unduly broad, but must be big enough to be meaningful. Your advisor and committee members are not supposed to know more about the topic than you do -- not individually, at least. Your dissertation is supposed to explain your findings and, along with the defense, demonstrate your mastery of the area in which you are now the leading expert. That does not mean writing everything you know -- it means writing enough about the most important points that others can agree with your conclusions.

Last of all, don't fall into the trap that ties up many a candidate, and causes some of them to flame out before completion: your thesis does not need to be revolutionary. It simply needs to be an incremental advancement in the field. Few Ph.D. dissertations have ever had a marked impact on the field. Instead, it is the set of publications and products of the author that may change the field.

If your dissertation is like most, it will only be read by your committee and some other Ph.D. candidates seeking to build on your work. As such, it does not need to be a masterwork of literature, nor does it need to solve a long-standing problem in computing. It merely needs to be correct, to be significant in the judgement of your committee, and it needs to be complete. We will all applaud when you change the world after graduation. And at that you will find that many well-known scientists in CS have made their careers in areas different from their dissertation topic. The dissertation is proof that you can find and present original results; your career and life after graduation will demonstrate the other concerns you might have about making an impact.

So get to work!

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