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CHAPTER 4: Observation 95four 30-minute periods every 2 hours. A random time-sampling technique couldbe used in the same situation by distributing four 30-minute periods randomlyover the course of the day. A different random schedule would be determinedfor each day observations are made. Times would vary from day to day, but,over the long run, behavior would be sampled equally from all times of theschool day.Electronic devices provide a major advantage in carrying out time samplingusing randomization. Electronic pagers can be programmed to signal observerson a random time schedule (normal sleeping times are excluded). For example,in their study of middle-class youth, Larson and others (Larson, Richards,Moneta, Holmbeck, & Duckett, 1996) obtained self-reports on adolescents’ experiencesat “16,477 random moments” in their lives. Systematic and randomtime-sampling procedures are often combined, as when observation intervalsare scheduled systematically but observations within an interval are made atrandom times. For example, electronic pagers might be programmed to signalevery 3 hours (systematic), but at a randomly selected time during each 3-hourinterval. Whatever time-sampling procedure is used, the goal of time samplingis to obtain a representative sample of behavior that will represent an organism’susual behavior.Time sampling is not an effective method for sampling behavior when theevent of interest occurs infrequently. Researchers who use time sampling forinfrequent events may miss the event entirely. Or, if the event lasts a longtime, time sampling may lead the researcher to miss an important portion ofthe event, such as its beginning or end. In event sampling the observer recordseach event that meets a predetermined definition. For example, researchers interestedin observing children’s reactions to special events in school, such as aholiday play, would use event sampling. The special event defines when theobservations are to be made.Event sampling also is useful for observing behavior during events thatoccur unpredictably, such as natural or technical disasters. Whenever possible,observers try to be present at those times when an event of interest occurs oris likely to occur. Although event sampling is an effective and efficient methodfor observing infrequent or unpredictable events, the use of event sampling caneasily introduce biases into the record of behavior. For instance, event samplingcould lead an observer to sample at the times that are most “convenient” oronly when an event is certain to occur. The resulting sample of behavior at thesetimes may not be representative of the same behavior at other times. There isyet another sampling procedure that also may be used to obtain a representativesample: situation sampling.Situation Sampling• Situation sampling involves studying behavior in different locations andunder different circumstances and conditions.• Situation sampling enhances the external validity of findings.• Within situations, subject sampling may be used to observe some people inthe setting.