The most sensitive, sophisticated, and flexible instrument of observation available today is the human being. All the recent advances in technology have not changed this central fact; we can monitor communications, transcribe conversations using language processing software, and conduct computer-assisted content analysis of the results. Still, at some point a person who understands the social context must infer the meaning of the communications. Systematic methods of observation may vary the unit of analysis, shift the boundaries of categories, and adjust the level of judgment allowed, but sociologists are ultimately left with the basic reality of human beings watching other human beings. The role of the methodologist is to make this process more systematic.

Most sociological data are filtered through the perceptions of informants in an idiosyncratic manner. Retrospective accounts of events, opinion polls, and surveys measure the output of the social perception process. Only systematic observation...