validity, external

n. External validity examines the extent to which conclusions drawn from a single study or target sample can be accurately generalized to the larger population, other populations, alternate settings, or alternate periods. External validity is concerned with unique factors that may have influenced the results of a particular study that would prevent findings from generalizing to other groups. As such, external validity may be negatively influenced by interactions between the way subjects are selected and their assignment to groups, unintentional effects of pretesting, unique factors of the research setting, participant reactance, or the cumulative impact of repeated measures. External validity is limited when samples or observations are selected or assigned in a nonrandom fashion; as such, external validity is generally low for case studies or single-subject methodology. External validity is increased through the use of randomization, replication, and extension. – BJM