It's interesting seeing my alma mater show up here. I wouldn't be surprised if Rolla students exhibited a higher rate of depression than the norm. Having spent 4 years there, I knew a lot of people that were bitter about being there. It's a small state engineering school in the middle of nowhere, without any particular pedigree or notoriety, known mostly, at least among other students in the midwest, for it's St. Patrick's Day festivities and drinking culture.
At any rate, I'd certainly want to see a sample from a different or at least more diverse population before I would think my browsing habits said anything about my general mental state. Beyond what was mentioned about, the sample at Rolla was presumably first- and second-year students living in the dorms as the rest would not be sharing an internet connection in a way that makes monitoring per student feasible.
It's part of the traditional split between quantitative and qualitative psychologists (and sociologists), each of whom gets one side of the equation stronger. The qualitative side typically goes "out into the world" and tries to interview a target community, building an understanding and iterating to fill in gaps in the understanding. They often succeed in quite good coverage, but don't produce statistical results. The quantitative side typically wants to measure statistically significant results on pre-specified, narrower questions, but often does so only on populations on convenience, rather than going "out into the world" and really understanding the populations that are out there.
Unfortunately, its not going to change, because of the pressures on academics to publish, publish, publish inclines them to take full advantage of these samples of convenience.
Its actually even worse, because the majority of psych papers are based on American psych students, so there's not even much of a good geographic spread in the ridiculously limited samples psychologists use.
Our university has about as high a percentage of Engineering and Science students as any university does. Again, don't quote me, but it has gotta be pretty darn close to the top.
http://web.archive.org/web/20070930201652/http://www.slate.c... - Missouri College Students: Are they really that miserable?
"For five of the past nine years, one of the three colleges—the University of Missouri-Columbia, Stephens College, and the University of Missouri-Rolla—has landed at No. 1 on the Princeton Review's list for the school with the 'least happy students.'"
(University of Missouri - Rolla being the former name of Missouri S&T.)