Demonstrated that time sampling is inaccurate for estimating durations or frequencies of behaviors. Also concluded that (1) individual or group differences can change depending on whether time sampling or continuous sampling is used; and (2) error rates are high when bout lengths of behaviors are short or when interval length is long. (BC)

A laboratory analogue of naturalistic observation was used to examine the relationship of observer drift to instructional set and experimenter status. Results indicated a highly significant decrease in observer reliability coinciding with the shift from training to data collection. (ST)