Assemble Your Application

Letters of Recommendation

The admissions committees is looking through your application to try to find reasons---specifically, evidence of your ability to do research (for PhD programs) or evidence of your ability to succeed in coursework (for MS programs)---to accept you into their program. The different parts of your application offer different opportunities for you to provide this sort of evidence to the committee.

Because the Letters of Recommendation (LOR) represent a review of your abilities provided by a (reasonably) unbiased 3rd party, these letters could provide compelling evidence of exactly the sort that the admissions committee is looking for. Depending on your circumstances, you may or may not be able to get these sorts of letters, but the strongest PhD applicants are sometimes accepted to top schools primarily on the strength of their Letters of recommendation (LOR), with all the other application materials playing a significantly less important role. For example, if there’s a single highly reputed professor (who’s credible and is well known to the admissions committee) that writes a strong letter enthusiastically endorsing your application, that by itself could be all the evidence the committee needs to admit you.

Here, we’ll describe what admissions committees are looking for in your LORs. If you’re trying to decide whom to ask for a letter, this will help you to make that decision. In addition, we will also give advice on how to provide information to your letter writers to maximize the odds of their writing you a strong letter.

Factors that make a strong LOR. For a letter of recommendation to help you get into a graduate program, the letter should ideally:

a. Be written by someone that knows your work well.
b. Be written by someone that thinks highly of you.
c. Be written by someone who can credibly evaluate PhD/MS applicants, and that the admissions committee has reason to trust.

All of the factors (a)-(c) should ideally be true for a letter to be considered a strong one. If even one of these is not true, then that makes the letter of recommendation worth much less. For example, if (b) and (c) are true, but not (a)--such as if you get a letter from a personal friend who likes you, is well known and is credible, but this person really doesn’t know your work well--then the letter won’t help much. If (a) and (b) are true, but not (c)--such as if you ask an inexperienced PhD student to write a letter--then it’s also difficult for the admissions committee to consider their letter strong to be evidence for admitting you.

If your only interaction with a professor is that you’ve taken a class from them--especially if it’s a large class where you and the professor had relatively few personal interactions--then it’s also less likely that they they know you well (factor a). Even if you did well and got an A+ in that class, there’s a good chance that the letter you’d get would be a form letter that basically says “This student took my class on topic X, and did well and got an A+ grade.” If you did a significant project in the class, and if the professor is willing to talk at length about your project, perhaps the letter could be somewhat helpful; but otherwise, the admissions committee could get almost the same information about your grade from your transcript. Some professors get a lot of requests for LORs from students that they don’t really know personally, but who had taken just a single class from them. In this case, they usually send a form letter (and it will be pretty obvious to the committee that this is a form letter), which will not help your application much.

The importance of factors (a) and (b) above when it comes to selecting your letter writers seems clear--you’d like the letter to be written by someone who knows your work well and thinks highly of it. The factors that the admissions committee considers for (c) are subtle, and is worthy of more discussion, which we provide next.

Selecting letter writers.The most credible letter--one that scores well on factor (c)--is one that’s written by someone who (i) is in a position where they frequently have to evaluate people (of a caliber comparable to those that would get admitted to the graduate program), and thus can tell the difference between strong and weak applicants, (ii) is familiar with what it takes to succeed in the sort of graduate program you’re applying to, and (iii) perhaps even is known to the admissions committee (this last item is rare, so don’t worry if you don’t know anyone that satisfies this). The vast majority of applicants will not have any letter writers that satisfy all of (i)-(iii) above, and many applicants will get admitted any such a letter from someone like this; we present this only to give you ideas to help your selection of letter writers.

To give an example, if you are applying to a PhD program in Computer Science, then a letter of recommendation from an experienced Computer Science professor from a good school, one who has an international reputation in research, would be considered a very credible one. This is because this professor is likely routinely evaluating dozens or hundreds of students each year, and thus can tell the difference between strong and weak students. He/she would also be familiar with what it takes to succeed in a top Computer Science program. If he/she is known either personally or by reputation to members of the admissions committee, then that can only further build trust in the admissions committee’s eyes of the LOR’s evaluation of your abilities. (Obviously, this professor must also know your work well and think highly of you; otherwise the letter won’t count for much.)

A letter from a very junior Assistant Professor, one who’s been a professor only for 1-2 years, might be trusted less than one from a more experienced professor, because the junior professor would not have evaluated that many students yet in their career, and thus be less able to give accurate evaluations. For this reason, letters from PhD students and post docs are also considered less credible. For PhD applications--where what matters most is your ability to do research--letters from faculty members that are at the forefront of their research area are also likely more credible than letters from faculty who are not active in research.

A letter from a professor working in the proposed area of research may also be somewhat more credible than one from a professor that works in an entirely different area. For example, if you are applying to a PhD program in Computer Science, and receive a strong letter from a medical school professor---one who has no experience in cutting-edge Computer Science research---then the letter will most likely help somewhat, but the committee may wonder just how well qualified your letter writer is to evaluate your ability to do Computer Science research. If however the medical school professor is involved in Computer Science research as well, or can otherwise be trusted to be familiar with Computer Science standards of research, then this is less of a concern.

If you currently working in industry and are applying to a PhD program, then a letter from your manager (depending on who she is) may or may not be considered credible in terms of being an accurate evaluation of your ability to do research. If your manager works in a good research lab or otherwise has an international research reputation, then their judgment may well be trusted by the committee. If on the other hand the manager is not familiar with what it’s like to do research at a good university, then it’s less likely that the admissions committee will consider her qualified to say whether or not you would do well in a PhD program. Indeed, if your manager doesn’t do research and seems unlikely to be able to get into a top PhD program herself, the committee would rightfully question her ability to judge whether or not you should get into one. If you are applying to an MS program however, then this may be less of a concern, and a strong letter from your manager reporting on your work in industry would still be helpful.

If you have worked on multiple projects with different people, it can be useful to select letter writers from different projects, so that each one can talk about a different aspect of your work, and give the admissions committee a fuller picture of your professional background.

Whereas strong letters can significantly help your application, weak letters don’t really hurt your application directly. For example, if you get two strong letters from Professor X and Professor Y, and end up with a neutral “form letter” from Professor Z that says “This applicant took my class and got an A grade”, then the letter from Professor Z won’t really hurt your application; instead, it just doesn’t present much evidence to the committee of your abilities, and thus doesn’t really help it either. Depending on how many professors you’ve worked with, it’s not uncommon to have one neutral, “non-helpful” letter. Of course, if Professor Z were to write a negative letter that actively criticizes you, then that could provide negative evidence to the committee for admitting you, and could really hurt your application; but this is rare and most letter writers will not do this.

Approaching potential letter writers.Sometimes, the best choice of letter writers is not obvious, and there’s a tradeoff among the factors (a)-(c) described earlier, as well as trying to get letters that cover the different projects you’ve worked on.

Sometimes, you might be uncertain as to just how highly someone thinks about your work, and thus whether or not they will write a strong letter for you. In this case, we suggest that you sound out your potential letter writers to try to get a sense of how likely they are to write a strong letter. Specifically, if they aren’t going to write a strong letter, then you really don’t want them to write one. It’s awkward to ask people directly if they’d be willing to write a strong letter (and many professors also don’t like being asked “will you be willing to write a strong letter?”, since it’s awkward to say no). A good alternative to this is to ask them if they’d be willing to write a letter, but give them an “easy out”--i.e., give them an easy way to say “no” to writing a letter in the event that they won’t write a strong letter.

For example, you could send an email to a professor saying:

From: You <>
To: Professor <>
Subject: Letter of recommendation?

Dear Professor Lee,

I’ll be applying to PhD [or MS] programs this fall, with applications due starting December 7th. As you might know, I’ve been working with Adam [a PhD student] on ABC methods for gene synthesis. I wasn’t sure how closely you’ve followed what I’ve been working on, but I was wondering if you might be sufficiently familiar with what I’d been doing to write a letter of recommendation?

If so, I’ll also send you a copy of my resume and research statement, and anything else that might be helpful for writing the letter.

Thank you,
Your name

By asking a professor if they’re “sufficiently familiar with your work to write a letter,” you’re giving them an easy way to say no if they aren’t enthusiastic about writing a letter, by simply saying that they’re just not that familiar with your work. If they aren’t enthusiastic about writing a letter, you probably want them to say no.

Of course, if your letter writer is someone that you’ve worked closely with (such as if it’s your direct mentor) and you’re pretty sure they’ll write a helpful letter, then there’s no need to dance around it like in the example above, and you should just politely and directly ask them for a letter.

Helping your letter writers write a strong letter. Having selected your letter writers and gotten them to agree to writing a letter, how do you help them write the strongest possible letter? Your letter writer is probably busy. If they’re a professor, they might be writing a dozen letters of recommendation a year. Perhaps they have only a vague recollection of what work you did, in which case their LOR would be similarly vague, which is not going to be helpful. Even if you worked closely with a professor, chances are they don’t remember all of the work you did and that you’d like to them talk about.

To get a strong letter, you should try to “prime” your letter writers to write a strong letter. Specifically, help out your letter writers by providing them a short document (sometimes called a “cheat sheet”) that contains a clear, succinct description of whatever it is you want to make sure they remember about you when writing the LOR. If you’ve worked with them on one or more projects, write a few paragraphs about the work you did with them (they almost certainly won’t remember all the details of what you did), describing your role and specific accomplishments on the project, and provide this to them. Make it easy for them to almost “cut-and-paste” from your description of the project into the letter you want them to write. If you have other significant projects that you’ve worked on with others, feel free to mention this too in the “cheat sheet.” If you once did a class project with them, but suspect that they no longer remember the project, provide to them a copy of your project report, to make it easy for them to refer to and write about it. f you have any major publications, or if you’ve won any major awards that they might not know about, or if you got an A+ in their class, let them know too. In other words, summarize everything you want your letter writer to remember or know about your, and provide this to them in an easy-to-read format.

Also provide to your letter writer your resume, and (if your grades/coursework is impressive) a copy of your transcript. Most students will also provide to the letter writer a draft of their research statement, though the “cheat sheet” (which is written just for the letter writer) usually does a letter job conveying to them what you really want them to remember.

Make sure your letters get sent in.Some admissions websites will show you if your letter writers have submitted their LORs; some others will send you email when an LOR is uploaded. After the application deadline, periodically check if your letter writers have submitted the LORs. It’s usually okay if an LOR is a few days late (admissions committees understand that letter writers sometimes submit late). But if an LOR is more than a few days late, or if it is missing entirely, then you’re missing out on an opportunity to provide information to the university,and this could hurt your application.

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