Contents

94 PART II: Descriptive MethodsSAMPLING BEHAVIOR• When a complete record of behavior cannot be obtained, researchers seek toobtain a representative sample of behavior.• The extent to which observations may be generalized (external validity)depends on how behavior is sampled.Key ConceptBefore conducting an observational study, researchers must make a numberof important decisions about when and where observations will be made.Because the investigator typically cannot observe all behavior, only certain behaviorsoccurring at particular times, in specific settings, and under particularconditions can be observed. In other words, behavior must be sampled. Thissample is used to represent the larger population of all possible behaviors. Bychoosing times, settings, and conditions for their observations that are representativeof a population of behaviors, researchers can generalize their findingsto that population. That is, results can be generalized only to participants, times,settings, and conditions similar to those in the study in which the observationswere made. The key feature of representative samples is that they are “like” thelarger population from which they are drawn. For example, observations madeof classroom behavior at the beginning of a school year may be representativeof behavior early in the school year, but may not yield results that are typical ofbehavior seen at the end of the school year.External validity refers to the extent to which the results of a research studycan be generalized to different populations, settings, and conditions. Recall thatvalidity concerns “truthfulness.” When we seek to establish the external validityof a study, we examine the extent to which a study’s findings may be usedaccurately to describe people, settings, and conditions beyond those used in thestudy. In this section we describe how time, event, and situation sampling areused to enhance the external validity of observational findings.Time Sampling• Time sampling refers to researchers choosing time intervals for makingobservations either systematically or randomly.• When researchers are interested in events that happen infrequently, theyrely on event sampling to sample behavior.Key ConceptResearchers typically use a combination of time sampling and situationsampling to identify representative samples of behavior. In time sampling, researchersseek representative samples by choosing various time intervals fortheir observations. Intervals may be selected systematically (e.g., observing thefirst day of each week), randomly, or both. Consider how time sampling couldbe used to observe children’s classroom behavior. If the researchers restrictedtheir observations to certain times of the day (say, mornings only), they wouldnot be able to generalize their findings to the rest of the school day. One approachto obtaining a representative sample is to schedule observation periodssystematically throughout the school day. Observations might be made during