Library of Congress call numbers group books by topic. The most important call number range for research in this subject are the following:
BF176: Psychological tests and testing.
BF180-198: Experimental psychology.
BF511-593: Affection. Feeling. Emotion.
BF712-724: Developmental psychology.
Other significant call number areas to look into are:
HF5548-5549: Industrial psychology.
HM711-806: Groups and organizations.
HM1001-1281: Social psychology.
LB1050-1091: Educational psychology.
R726: Medicine in relation to psychology.
RC321-571: Neurosciences. Psychiatry.
There are many other call ranges that specifically relate to groups of people in terms of ethnic identity, culture, gender, and social issues. Take a look at the Sociology & Anthropology research guide for more possibilities.