I went into character creation with no pre-conceived notions about what I wanted, or what I 'should' end up with, so I literally cycled through all of the options until I saw something I liked. In this case, a male Au'ra for gender and race. The prompt for that? The dopamine release in my brain when I laid eyes on the one I liked the most.
I don't mean to be flippant, or insinuate that what I said should be obvious to most. In fact, I only state it because many people don't think about 'liking something' in this way, but IMHO a collegiate-level paper should probably take it into consideration, or at least speak of it. There's simple science behind why we 'like' things, and quite interestingly, we as individuals we have zero control over that science. You either like something or you don't. You cannot choose what you do and don't like. I find that fascinating.
Think of your favorite food. Now, why do you like it? Say you give the response 'it's nice and savory,' or 'it's creamy and sweet.' Well, why do you like 'savory' or 'sweet'? You don't really know. You just like it, because when that particular taste touches your tongue, your brain releases a whole bunch of dopamine. Ditto why you like shows, books, movies, music, why you fall in love, etc., etc.
But, I do get what you're after. So, to put it in common terms, the fact that I found these choices to be aesthetically pleasing is why I chose them. I've created a couple different characters of varying races and genders and appearances, and I also chose those races, genders and appearances on what I thought looked good.
Is there any other reason for choosing a particular race, gender, etc? Every response in this thread so far can be attributed to dopamine release, from the people that like cats, to the people that chose based on Anime, to the people that used pertinent dates to choose.
Do some people choose races and genders and appearances which they don't like, or which they find aesthetically displeasing? Perhaps for some niche RP, but it would be a small percentage. I think it would be incredibly interesting to add a chapter to your paper on people who play characters they don't like, because of some external pressure.
I know I got way deeper than you wanted. My apologies; I'm a junkie for science, knowledge and conjecture surrounding both. Good luck on your paper.