Hi, Daystar
Very little actual scholarly research has been done in regards to the psychological trends of Jehovah's Witnesses, primarily because to do so requires a lot of data, especially things like statistics from psychiatric wards, private psychologists practices, suicide reports, etcetera, which are simply not there, mainly because JWs go to such lengths to avoid "worldly" disciplines like psychology. Another problem, along the same lines, is that it would be impossible to convince an adequate number of active Jehovah's Witnesses to participate in an experimental study. One could try to conduct an experiment without obtaining their consent, but this kind of research would be shot down immediately in the scholarly world as unethical.
You also have the option of trying to find enough willing ex-JWs to participate in a study, but again, you will have trouble with the validity of your hypothesis and conclusion because you'll be gathering data from those people who have left, not those who have chosen to stick it out with the WTS. Something about those with the strength to leave is fundamentally different from those who choose to stay, so the only conclusions you could draw would be about what an active JW might NOT be.
So.... that leaves you with case studies, which are fascinating, but since they are simply portraits of individuals or small groups of individuals, and don't involve any sort of hypothesizing end testing of the hypothesis' prediction, isn't scientific and can't be generalized to the larger JW population.
Not all hope is lost, though! Several very good scholarly studies in the field of sociology have been done on Jehovah's Witnesses, which might actually be more informative because anyone who has been around JWs or the WTS knows that they tend to think and act not as individuals, but as a group, and since Sociology is about studying group processes, it works!
Check out "Jehovah's Witnesses: Portait of a Contemporary Religous Movement" by Andrew Holden. It touches lightly on personality trends that the researcher noted in his field studies. It also contains a long bibliography of other great works from the past. This book is the most contemporary that I've been able to find, published I think in 2002.
Sorry to be so long-winded! Hope this helps...