Psychology, originally the branch of philosophy dealing with the mind, then the science of mind, and now, considered in its more general context, the science of behavior, whether human or animal, and of human thought processes. Psychology is closely connected with medicine, psychiatry, and sociology. There are a number of closely interrelated branches of human psychology. Experimental psychology embraces all psychological investigations undertaken by the psychologist. The experiments may center on the individual or on a group, in which latter case statistics will play a large part in the research. Social psychologists use statistical and other methods to investigate the effect of the group on the behavior of the individual. In applied psychology, the discoveries and theories of psychology are put to practical use, as in industrial psychology. Comparative psychology deals with the different behavioral organizations of animals, including humans. Physiological psychology attempts to understand the neurology and physiology of behavior. Clinical psychologists diagnose and treat mental disorders, principally using psychological tests, psychotherapy, and behavior therapy. They also do research on psychological factors affecting mental illness.