Social psychology is the study of how the thoughts, feelings, and behavior of individuals are influenced by the actual, imagined, or implied presence of other people. Social psychologists examine how situations and people combine to affect what people think, feel, and do. Studies and experiments by social psychologists have produced many important findings about human behavior. Social psychologists investigate a wide variety of social interactions and behaviors. These include how people form impressions of themselves and others, stereotyping and prejudice, leadership and group behavior, altruism (concern or help for others), the formation of close personal relationships, and aggression.