Is it worthwhile to diversify your rec letters?

[Zaphod2020]

I'm trying to pick my 3 recommendation letter writers and find myself with 2 options:

1. Have 3 pure math professors write my letters.

2. Have 2 pure math professors and 1 humanities professor write my letters.

For context, I attended a small liberal arts college and have strong relationships with all 4 professors in question. My humanities professor, however, definitely knows me best and will likely have the most meaningful things to say. As such, I was wondering if statistics admissions committees value the perspective of professors from outside of math/statistics/CS at all or if a letter from a humanities professor will mean essentially nothing to them.

Thanks!

[TakeruK]

Generally, letters are requested because the committee wants to hear from their colleagues on whether or not you would be a successful researcher and student in their graduate program. The letter writers are often asked to evaluate your abilities in coursework and research in their field. Sometimes they are asked to compare you to other students in their department. Note that for the most part, these letters are not "character references".

So, with the information provided here, it's not really clear how the humanities professor can write a more relevant letter than a third math professor. That said, there are some situations where a letter from the humanities prof can be really useful:

1. You had some personal or academic situation that can be best explained by the humanities prof. For example, if you had to take a leave of absence and/or your grades in one semester suffered due to some personal situation and the humanities prof can explain this because they knew you best, then a letter from them could be helpful. Or, perhaps you began your degree intending to major in the humanities but changed track. If you did really well in the earlier track then the humanities prof can provide a different perspective of your excellence. Or, if the change caused you to take an extra year or have otherwise weird academic track, the prof can comment on that.

2. You did some research work or some impressive coursework with the professor in humanities and the prof can highlight this.

3. You know that the department you are applying to places particular extra value in their students having cross-disciplinary talents and/or you are applying to a multi-disciplinary area of work. Note that these departments are not the norm, i.e. there aren't very many "liberal arts college" equivalents in grad school. 

If some of the above apply, then it might be worth considering either sending the 3 math letters and an extra humanities letter or 2 math + 1 humanities if you cannot submit more than 3 letters.

However, before you do any of this, have you had a long conversation with your letter writers about grad school applications yet? You say you have strong relationships with them so hopefully that means they are willing to sit down with you to talk about grad school and letters. Usually they will ask who else are you asking for letters. If you start with the two math profs that you would ask no matter what, then you can ask them whether they think a 3rd letter from a humanities prof instead of a math prof would be a good idea. And you can ask whether having an extra letter from the humanities prof instead of just 3 math letters would be better. 

[lemma]

Wait, if you have a leave of absence, do you have to explain it? I sent off an application yesterday which didn't address it at all. I only took a semester off, and graduated two months later than originally scheduled. 

[TakeruK]

5 hours ago, lemma said:

Wait, if you have a leave of absence, do you have to explain it? I sent off an application yesterday which didn't address it at all. I only took a semester off, and graduated two months later than originally scheduled. 

No, you do not have to address it**, and one semester is not a long leave at all. Some applicants might choose to address it to provide a continuous narrative of what they did, in the same way as a cover letter for a job application might address gaps in employment as seen on the resume. 

If you took a leave to do something that you want to share (e.g. work in the industry, try to start a business, star in a TV show, etc.) then you might also want to address it. If it's a personal/health/family reason then I think it's up to you to decide if you want to mention it. For just one semester off, that level of personal detail isn't really necessary.

The context of my point above might be something like a personal or health situation caused you to spend less time on academics to address the other priorities in your life. Your grades might drop or you might have switched to part-time status. Then maybe you decided that you needed some time completely off from academics. In this case, it's probably a good idea to mention the scenario in your application. Writing a couple of sentences in the SOP is fine but some applicants might feel that they are just "making excuses" and might be more comfortable with a letter writer who knew the student during this time to discuss it instead.

(** In general. Some applications might have specific instructions that require you to do so.)