POPULATION VALIDITYPopulation validity is a type of external validity which describes how well the sample used can be extrapolated to a population as a whole.It evaluates whether the sample population represents the entire population, and also whether the sampling method is acceptable. For example, an educational study that looked at a single school could not be generalized to cover children at every US school. On the other hand, a federally appointed study, that tested every pupil of a certain age group, will have exceptionally strong population validity. Due to time and cost restraints, most studies lie somewhere between these two extremes, and researchers pay extreme attention to their sampling techniques. Experienced scientists ensure that their sample groups are as representative as possible, striving to use random selection rather than convenience sampling.
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