Last month, we offered suggestions on how to prepare for your thesis defence: Decide whether you need more research results, sketch out a plan for those experiments and for writing thesis chapters, and--importantly--get your supervisor's support for that plan. Now it's time to wrap things up in the lab and start writing.
Writing a thesis is easier said than done, of course, and you have plenty of work ahead. But like any big undertaking, writing a thesis is easier if you break it down into smaller steps.
First things first
If you haven't already made a countdown plan as described in last month's column, start with that first. Then, before you start writing, make sure you and your supervisor agree on the table of contents. This might seem obvious, but we have seen too many students start working on chapters only to have those chapters tossed out later.
Cut the problem down to size
Once you've decided on a table of contents, it's time to expand it into a detailed outline. Your outline will be several pages long and consist of chapter headings, subheadings, figure and table titles, some key words, and essential comments. Your outline will keep you on track and provide you with a framework for the text. It also forces you to break up the writing into manageable pieces.
Determine the format
Your department or university may have a standard format for your thesis. If so, there's probably a standard template you should use. If not, save yourself frustration and time by copying the format from a thesis that appeals to you. Make sure the format or template is easy to use. Once you've sent your thesis to your committee for review, you may consider upgrading your layout. For now, factor the format into your plan, but don't make it your primary concern.
While we're on the subject of format, be sure to use the proper citation format for your list of references. This list can run into the hundreds, so use the approved format for citing literature from the very beginning--both in the text and for the list of the references at the end. Use a good citation-manager program and enter all the information for every article referenced--including titles. You won't want to have to go back and redo this if you've done it wrong!
Transform published articles into thesis chapters
Before you delve into the chapters you have to write from scratch, start by transforming your published articles and submitted manuscripts into thesis chapters. It's not just a matter of stapling your papers together and sticking them into your thesis, however. You'll need to break the publications into pieces and weave them into a cohesive narrative, making sure the various parts fit together nicely without redundancies or gaps in logic. When doing this, keep the following in mind:
Drastically cut back or rewrite the introduction section of each article. There is no need to repeat what you will have already explained in the general introduction and literature survey of your thesis. Don't just delete those introductions, however; parts of your manuscript intros will be useful for your thesis introduction, so paste any relevant text into the intro section of your thesis outline for later editing.
Cut the Materials and Methods section as necessary to avoid repetition with other chapters. Again, you'll probably want to paste some of the Materials and Methods text into the relevant sections in your thesis.
Include text that may have been cut from the final version of the article due to space restrictions.
Update your literature citations (see above).
If someone else wrote one of your publications (i.e., you did the experiments but a more senior person wrote the manuscript), we suggest you rewrite the bulk of the text in your own words. Even if experiments were done in collaboration, a thesis has only one author--you--and the words in it should be yours.
After you've transformed your published articles into chapters, you will have to write new material for the remaining chapters. When you first start writing, it helps to begin with an easy section. This will give you confidence and get you into the writing habit. Because the methodology chapter is relatively straightforward, you might want to start with that one. If you've already written several methodology sections for your peer-reviewed articles, it won't take much time to prepare a first draft for your thesis.
Because a thesis has fewer space restrictions, you should take the opportunity to describe the details of your work that did not make it into published articles. In a thesis, it is better to err on the side of being too detailed than to risk leaving out crucial information. Be generous to the next generation of researchers; a detailed description of your progress and failures will save them a lot of time.
Writing up that last set of experiments
Now that you have worked your way through the initial chapters and have written most of your thesis, it is time to tackle writing up your final project. You probably haven't written an article on this research yet, so you'll need to decide whether to write the article first and then transform it into a chapter or do it the other way around.
If there is stiff competition in your field, your supervisor will probably insist that you write the article first. Otherwise, we suggest that you write the chapter first, as this approach will allow you to describe your work in detail. While the thesis is out for review with your dissertation committee, you can select the appropriate parts from the chapter and transform it into an article to submit to a peer-reviewed journal.
10 Tips for a Stress-Free Thesis
The introduction: The final hurdle
Although it comes first, the introduction will probably be the last chapter you write. The introduction is where you need to place your work in a broader context, explaining why the research is relevant to the scientific community and (assuming it is) to society.
Start thinking about your introduction long before you start writing your thesis. During your final year--or even earlier--create a file in which you collect ideas and article clippings that could be useful for the introduction. A file of good ideas will be a big help in writing a comprehensive and elegant introduction when the pressure is on.
The summary is the one section of your thesis that is sure to be read widely. In a few pages you will have to describe the main findings of your thesis research, so it is best to write this part after you have finished all the other chapters. Do not try to describe all your results in the summary--you're simply summarizing the bulk of your work. Be sure to designate in the summary which chapters contain particular findings.
Safeguard your work
We shouldn't have to remind you to back up your work, but we will anyway. Keep a copy of your thesis on an external hard drive, memory stick, or some other storage device. Back up daily and keep the copy (or copies) in a safe place. For extra security, keep a copy of your work-in-progress off-site on a remote server (in the event of fire or theft). The simplest way to do this is to open a Web-based e-mail account and regularly e-mail your work to yourself. There are also companies that offer online document-storage services.
Going for gold: Writing an error-free thesis
Because a thesis is usually written under severe time constraints, it is difficult to produce one without some typos and other minor errors. Spell checkers help, but they can't catch errors in those hard-to-spell technical terms. In addition, errors of grammar and syntax are not always highlighted, and minor scientific errors can be easily overlooked. Your goal, of course, is to have as few errors as possible.
We suggest you do two things to help make this a reality. First, put the manuscript aside for a short while after you've written the first draft. Once you've gained some distance from the material, read it over again with a sharp eye--not for content, but as a proofreader looking for typographical errors. Second, give a copy of your thesis to one or two trusted peers to read. Devise a creative way to reward them for every error they find (free cups of coffee or beer, or pizza, for example). This will give them an incentive to go through your thesis with a fine-toothed comb. If you can afford it, you may even consider hiring a professional copy editor to do this for you.
Most importantly, while writing your thesis, be sure to take care of yourself. Eat well, exercise, and get plenty of sleep so you're at your best when you sit down every day to write. This is the home stretch of your Ph.D., and you want to make sure you cross the finish line energized and ready for the next step.
Patricia Gosling and Bart Noordam are the authors of Mastering Your Ph.D.: Survival and Success in the Doctoral Years and Beyond (Springer, 2006). Gosling is a senior medical writer at Novartis Vaccines and Diagnostics in Germany and freelance science writer. Noordam is a professor of physics at the University of Amsterdam, the Netherlands, and director of a regional audit organization. He has also worked for McKinsey and Co.
Images. Top: Paul Worthington. Middle: courtesy, Springer.
Comments, suggestions? Please send your feedback to our editor.
Patricia Gosling is a coauthor of Mastering Your Ph.D.: Survival and Success in the Doctoral Years and Beyond (Springer, 2006). Gosling is a senior medical writer at CMPMedica in Malaysia and a freelance science writer.
Bart Noordam is a coauthor of Mastering Your Ph.D.: Survival and Success in the Doctoral Years and Beyond (Springer, 2006). He is a professor of physics at the University of Amsterdam, the Netherlands, and director of a regional audit organization. He has also worked for McKinsey & Co.
To The Candidate:
So, you are preparing to write a Ph.D. dissertation in an experimental area of Computer Science. Unless you have written many formal documents before, you are in for a surprise: it's difficult!
There are two possible paths to success:
- Planning Ahead.
Few take this path. The few who do leave the University so quickly that they are hardly noticed. If you want to make a lasting impression and have a long career as a graduate student, do not choose it.
All you really have to do is outlast your doctoral committee. The good news is that they are much older than you, so you can guess who will eventually expire first. The bad news is that they are more practiced at this game (after all, they persevered in the face of their doctoral committee, didn't they?).
Here are a few guidelines that may help you when you finally get serious about writing. The list goes on forever; you probably won't want to read it all at once. But, please read it before you write anything.
The General Idea:
- A thesis is a hypothesis or conjecture.
- A PhD dissertation is a lengthy, formal document that argues in defense of a particular thesis. (So many people use the term ``thesis'' to refer to the document that a current dictionary now includes it as the third meaning of ``thesis'').
- Two important adjectives used to describe a dissertation are ``original'' and ``substantial.'' The research performed to support a thesis must be both, and the dissertation must show it to be so. In particular, a dissertation highlights original contributions.
- The scientific method means starting with a hypothesis and then collecting evidence to support or deny it. Before one can write a dissertation defending a particular thesis, one must collect evidence that supports it. Thus, the most difficult aspect of writing a dissertation consists of organizing the evidence and associated discussions into a coherent form.
- The essence of a dissertation is critical thinking, not experimental data. Analysis and concepts form the heart of the work.
- A dissertation concentrates on principles: it states the lessons learned, and not merely the facts behind them.
- In general, every statement in a dissertation must be supported either by a reference to published scientific literature or by original work. Moreover, a dissertation does not repeat the details of critical thinking and analysis found in published sources; it uses the results as fact and refers the reader to the source for further details.
- Each sentence in a dissertation must be complete and correct in a grammatical sense. Moreover, a dissertation must satisfy the stringent rules of formal grammar (e.g., no contractions, no colloquialisms, no slurs, no undefined technical jargon, no hidden jokes, and no slang, even when such terms or phrases are in common use in the spoken language). Indeed, the writing in a dissertaton must be crystal clear. Shades of meaning matter; the terminology and prose must make fine distinctions. The words must convey exactly the meaning intended, nothing more and nothing less.
- Each statement in a dissertation must be correct and defensible in a logical and scientific sense. Moreover, the discussions in a dissertation must satisfy the most stringent rules of logic applied to mathematics and science.
What One Should Learn From The Exercise:
- All scientists need to communicate discoveries; the PhD dissertation provides training for communication with other scientists.
- Writing a dissertation requires a student to think deeply, to organize technical discussion, to muster arguments that will convince other scientists, and to follow rules for rigorous, formal presentation of the arguments and discussion.
A Rule Of Thumb:
Good writing is essential in a dissertation. However, good writing cannot compensate for a paucity of ideas or concepts. Quite the contrary, a clear presentation always exposes weaknesses.
Definitions And Terminology:
- Each technical term used in a dissertation must be defined either by a reference to a previously published definition (for standard terms with their usual meaning) or by a precise, unambiguous definition that appears before the term is used (for a new term or a standard term used in an unusual way).
- Each term should be used in one and only one way throughout the dissertation.
- The easiest way to avoid a long series of definitions is to include a statement: ``the terminology used throughout this document follows that given in [CITATION].'' Then, only define exceptions.
- The introductory chapter can give the intuition (i.e., informal definitions) of terms provided they are defined more precisely later.
Terms And Phrases To Avoid:
- Mostly, they are very often overly used. Use strong words instead. For example, one could say, ``Writers abuse adverbs.''
- jokes or puns
- They have no place in a formal document.
- ``bad'', ``good'', ``nice'', ``terrible'', ``stupid''
- A scientific dissertation does not make moral judgements. Use ``incorrect/correct'' to refer to factual correctness or errors. Use precise words or phrases to assess quality (e.g., ``method A requires less computation than method B''). In general, one should avoid all qualitative judgements.
- ``true'', ``pure'',
- In the sense of ``good'' (it is judgemental).
- ``an ideal solution''
- ``today'', ``modern times''
- Today is tomorrow's yesterday.
- How soon? Later tonight? Next decade?
- ``we were surprised to learn...''
- Even if you were, so what?
- ``seems'', ``seemingly'',
- It doesn't matter how something appears;
- ``would seem to show''
- all that matters are the facts.
- ``in terms of''
- ``based on'', ``X-based'', ``as the basis of''
- Does not mean ``various''; different than what?
- ``in light of''
- ``lots of''
- ``kind of''
- ``type of''
- ``something like''
- ``just about''
- ``number of''
- vague; do you mean ``some'', ``many'', or ``most''? A quantative statement is preferable.
- ``due to''
- only if you know the statistical probability (if you do, state it quantatively
- ``obviously, clearly''
- be careful: obvious/clear to everyone?
- Can have a negative connotation, as in ``simpleton''
- ``along with''
- ``actually, really''
- define terms precisely to eliminate the need to clarify
- ``the fact that''
- makes it a meta-sentence; rephrase
- ``this'', ``that''
- As in ``This causes concern.'' Reason: ``this'' can refer to the subject of the previous sentence, the entire previous sentence, the entire previous paragraph, the entire previous section, etc. More important, it can be interpreted in the concrete sense or in the meta-sense. For example, in: ``X does Y. This means ...'' the reader can assume ``this'' refers to Y or to the fact that X does it. Even when restricted (e.g., ``this computation...''), the phrase is weak and often ambiguous.
- ``You will read about...''
- The second person has no place in a formal dissertation.
- ``I will describe...''
- The first person has no place in a formal dissertation. If self-reference is essential, phrase it as ``Section 10 describes...''
- ``we'' as in ``we see that''
- A trap to avoid. Reason: almost any sentence can be written to begin with ``we'' because ``we'' can refer to: the reader and author, the author and advisor, the author and research team, experimental computer scientists, the entire computer science community, the science community, or some other unspecified group.
- ``Hopefully, the program...''
- Computer programs don't hope, not unless they implement AI systems. By the way, if you are writing an AI thesis, talk to someone else: AI people have their own system of rules.
- ``...a famous researcher...''
- It doesn't matter who said it or who did it. In fact, such statements prejudice the reader.
- Be Careful When Using ``few, most, all, any, every''.
- A dissertation is precise. If a sentence says ``Most computer systems contain X'', you must be able to defend it. Are you sure you really know the facts? How many computers were built and sold yesterday?
- ``must'', ``always''
- ``proof'', ``prove''
- Would a mathematician agree that it's a proof?
- Used in the sense of ``prove''. To ``show'' something, you need to provide a formal proof.
- Your mother probably told you the difference.
- Use active constructions. For example, say ``the operating system starts the device'' instead of ``the device is started by the operating system.''
- Write in the present tense. For example, say ``The system writes a page to the disk and then uses the frame...'' instead of ``The system will use the frame after it wrote the page to disk...''
Define Negation Early:
- Example: say ``no data block waits on the output queue'' instead of ``a data block awaiting output is not on the queue.''
Grammar And Logic:
- Be careful that the subject of each sentence really does what the verb says it does. Saying ``Programs must make procedure calls using the X instruction'' is not the same as saying ``Programs must use the X instruction when they call a procedure.'' In fact, the first is patently false! Another example: ``RPC requires programs to transmit large packets'' is not the same as ``RPC requires a mechanism that allows programs to transmit large packets.''
All computer scientists should know the rules of logic. Unfortunately the rules are more difficult to follow when the language of discourse is English instead of mathematical symbols. For example, the sentence ``There is a compiler that translates the N languages by...'' means a single compiler exists that handles all the languages, while the sentence ``For each of the N languages, there is a compiler that translates...'' means that there may be 1 compiler, 2 compilers, or N compilers. When written using mathematical symbols, the difference are obvious because ``for all'' and ``there exists'' are reversed.
Focus On Results And Not The People/Circumstances In Which They Were Obtained:
- ``After working eight hours in the lab that night, we realized...'' has no place in the dissertation. It doesn't matter when you realized it or how long you worked to obtain the answer. Another example: ``Jim and I arrived at the numbers shown in Table 3 by measuring...'' Put an acknowledgement to Jim in the dissertation, but do not include names (even your own) in the main body. You may be tempted to document a long series of experiments that produced nothing or a coincidence that resulted in success. Avoid it completely. In particular, do not document seemingly mystical influences (e.g., ``if that cat had not crawled through the hole in the floor, we might not have discovered the power supply error indicator on the network bridge''). Never attribute such events to mystical causes or imply that strange forces may have affected your results. Summary: stick to the plain facts. Describe the results without dwelling on your reactions or events that helped you achieve them.
Avoid Self-Assessment (both praise and criticism):
- Both of the following examples are incorrect: ``The method outlined in Section 2 represents a major breakthrough in the design of distributed systems because...'' ``Although the technique in the next section is not earthshaking,...''
References To Extant Work:
- One always cites papers, not authors. Thus, one uses a singular verb to refer to a paper even though it has multiple authors. For example ``Johnson and Smith [J&S90] reports that...''
Avoid the phrase ``the authors claim that X''. The use of ``claim'' casts doubt on ``X'' because it references the authors' thoughts instead of the facts. If you agree ``X'' is correct, simply state ``X'' followed by a reference. If one absolutely must reference a paper instead of a result, say ``the paper states that...'' or ``Johnson and Smith [J&S 90] presents evidence that...''.
Concept Vs. Instance:
- A reader can become confused when a concept and an instance of it are blurred. Common examples include: an algorithm and a particular program that implements it, a programming language and a compiler, a general abstraction and its particular implementation in a computer system, a data structure and a particular instance of it in memory.
Terminology For Concepts And Abstractions
- When defining the terminology for a concept, be careful to decide precisely how the idea translates to an implementation. Consider the following discussion:
VM systems include a concept known as an address space. The system dynamically creates an address space when a program needs one, and destroys an address space when the program that created the space has finished using it. A VM system uses a small, finite number to identify each address space. Conceptually, one understands that each new address space should have a new identifier. However, if a VM system executes so long that it exhausts all possible address space identifiers, it must reuse a number.
The important point is that the discussion only makes sense because it defines ``address space'' independently from ``address space identifier''. If one expects to discuss the differences between a concept and its implementation, the definitions must allow such a distinction.
Knowledge Vs. Data
- The facts that result from an experiment are called ``data''. The term ``knowledge'' implies that the facts have been analyzed, condensed, or combined with facts from other experiments to produce useful information.
Cause and Effect:
- A dissertation must carefully separate cause-effect relationships from simple statistical correlations. For example, even if all computer programs written in Professor X's lab require more memory than the computer programs written in Professor Y's lab, it may not have anything to do with the professors or the lab or the programmers (e.g., maybe the people working in professor X's lab are working on applications that require more memory than the applications in professor Y's lab).
Drawing Only Warranted Conclusions:
- One must be careful to only draw conclusions that the evidence supports. For example, if programs run much slower on computer A than on computer B, one cannot conclude that the processor in A is slower than the processor in B unless one has ruled out all differences in the computers' operating systems, input or output devices, memory size, memory cache, or internal bus bandwidth. In fact, one must still refrain from judgement unless one has the results from a controlled experiment (e.g., running a set of several programs many times, each when the computer is otherwise idle). Even if the cause of some phenomenon seems obvious, one cannot draw a conclusion without solid, supporting evidence.
Commerce and Science:
- In a scientific dissertation, one never draws conclusions about the economic viability or commercial success of an idea/method, nor does one speculate about the history of development or origins of an idea. A scientist must remain objective about the merits of an idea independent of its commercial popularity. In particular, a scientist never assumes that commercial success is a valid measure of merit (many popular products are neither well-designed nor well-engineered). Thus, statements such as ``over four hundred vendors make products using technique Y'' are irrelevant in a dissertation.
Politics And Science:
- A scientist avoids all political influence when assessing ideas. Obviously, it should not matter whether government bodies, political parties, religious groups, or other organizations endorse an idea. More important and often overlooked, it does not matter whether an idea originated with a scientist who has already won a Nobel prize or a first-year graduate student. One must assess the idea independent of the source.
- In general, every dissertation must define the problem that motivated the research, tell why that problem is important, tell what others have done, describe the new contribution, document the experiments that validate the contribution, and draw conclusions. There is no canonical organization for a dissertation; each is unique. However, novices writing a dissertation in the experimental areas of CS may find the following example a good starting point:
Chapter 1: Introduction
- An overview of the problem; why it is important; a summary of extant work and a statement of your hypothesis or specific question to be explored. Make it readable by anyone.
Chapter 2: Definitions
- New terms only. Make the definitions precise, concise, and unambiguous.
Chapter 3: Conceptual Model
- Describe the central concept underlying your work. Make it a ``theme'' that ties together all your arguments. It should provide an answer to the question posed in the introduction at a conceptual level. If necessary, add another chapter to give additional reasoning about the problem or its solution.
Chapter 4: Experimental Measurements
- Describe the results of experiments that provide evidence in support of your thesis. Usually experiments either emphasize proof-of-concept (demonstrating the viability of a method/technique) or efficiency (demonstrating that a method/technique provides better performance than those that exist).
Chapter 5: Corollaries And Consequences
- Describe variations, extensions, or other applications of the central idea.
Chapter 6: Conclusions
- Summarize what was learned and how it can be applied. Mention the possibilities for future research.
- A short (few paragraphs) summary of the the dissertation. Describe the problem and the research approach. Emphasize the original contributions.
Suggested Order For Writing:
- The easiest way to build a dissertation is inside-out. Begin by writing the chapters that describe your research (3, 4, and 5 in the above outline). Collect terms as they arise and keep a definition for each. Define each technical term, even if you use it in a conventional manner.
Organize the definitions into a separate chapter. Make the definitions precise and formal. Review later chapters to verify that each use of a technical term adheres to its definition. After reading the middle chapters to verify terminology, write the conclusions. Write the introduction next. Finally, complete an abstract.
Key To Success:
- By the way, there is a key to success: practice. No one ever learned to write by reading essays like this. Instead, you need to practice, practice, practice. Every day.
- We leave you with the following ideas to mull over. If they don't mean anything to you now, revisit them after you finish writing a dissertation.
- After great pain, a formal feeling comes.
A man may write at any time, if he will set himself doggedly to it.
Keep right on to the end of the road.
The average Ph.D. thesis is nothing but the transference of bones from one graveyard to another.