The concepts reviewed here amount to a minimum standard vocabulary shared by sociologists. The discipline has expanded in so many different directions, however, creating specialties and subfields employing such a variety of research methods and theoretical approaches, that heterogeneity rather than a single coherent point of view has become its outstanding characteristic. Criminology and demography have both become virtually autonomous specialties within sociology, especially in the United States. Criminology has been penetrated by more-general sociological concerns and has tended to become part of the broader study of all kinds of deviant behavior, including those not involving violations of the law. In demography the study of fertility and of migration has been greatly influenced by sociological ideas, but the analysis of mortality and the application of mathematical models to population growth and change are more closely tied to other disciplines.
Sociologists are also active in some subfields that are fully interdisciplinary.
The oldest and most important of these subfields is social psychology, which is virtually a separate discipline in its own right, drawing practitioners from both sociology and psychology. Psychoanalytic ideas derived from Sigmund Freud and later psychoanalysts have been particularly influential in this last field of social psychology. A newer interdisciplinary subfield is sociobiology, which investigates the causal relations between the human genetic constitution and social behavior. Methods Sociologists make use of nearly all the methods used in the other social sciences and the humanities, from advanced mathematical statistics to the interpretation of texts. Quantitative methods, increasingly refined and adapted to computer technology, continue to play a central role in the discipline, tending to predominate, at least in the United States, in the research reported in sociology journals.