The experiment is most commonly used in conceptual research to determine the causal factors responsible for behavioral variations. It is also used in system-oriented research to compare alternative technologies and methods. The experiment is the most well known of objective measurement methods, although there are other ways of securing objective data, such as those described in the last part of the chapter: the simulated test of personnel capability, automatic performance recording, and analysis of archival data (from both epidemiological sources and from HF research).