Since its inception, sociological epistemologies, methods, and frames of enquiry, have significantly expanded and diverged. Sociologists use a diversity of research methods, collect both quantitative and qualitative data, draw upon empirical techniques, and engage critical theory. Common modern methods include case studies, historical research, interviewing, participant observation, social network analysis, survey research, statistical analysis, and model building, among other approaches. Since the late 1970s, many sociologists have tried to make the discipline useful for purposes beyond the academy. The results of sociological research aid educators, lawmakers, administrators, developers, and others interested in resolving social problems and formulating public policy, through subdisciplinary areas such as evaluation research, methodological assessment, and public sociology.