Should one avoid erudite vocabulary in statement of purpose? I am not a psychology major. 

I came across this paper
that shows that using erudite vocabulary will not do one good.

What makes me want to ask here is a case study in the paper. Long story short, a bunch of admission officers, unaware of being tested, reviewed the application documents such as statements of purpose and were asked to rate them. It turned out that those documents using big, learned words instead got somewhat lower rating than those using simple, direct words.

Though this research seems convincing, my concern is: Is this phenomenon general enough to suggest one should avoid using erudite vocabulary if one does not use the erudite words in an affected way?

If you are experienced admission reviewers, would you please throw some light or insights on this issue?
Erudition and eloquence are useful tools for academics to possess.

However, excessively erudite writing can become opaque. That's not what you want to achieve in scholarly writing. Scholarly writing should be lucid, informative, and as direct as possible. Thus, using "five-dollar" vocabulary when "fifty-cent" words will do probably distracts from your writing overall. On the other hand, if that five-dollar word is exactly the word you need in a given situation, don't be afraid to use it. It's better, in my opinion, to moderately challenge the reader in a concisely written text than to be long-winded.