The Theory Of Meta-Analysis—Sampling Error and the Law Of Small Numbers
Although not widely known, the meta-analytic technique is actually founded on a sound conceptual basis. That conceptual basis is sampling error theory. In psychometric terms, sampling error is the difference between the characteristics of a sample and those of the population from which that sample was drawn. Sampling error occurs because a sample typically represents only a small fraction of the original population. For example, if a study pertains to general human nature such as sex differences for a given personality characteristic, then a typical sample of 50 represents a meager 0.0000008 percent of the general human population of 6 billion. In such a case, any permutation of results and outcomes can and does occur, such as the effect in the sample being slightly stronger, considerably stronger, slightly weaker, or considerably weaker than the true effect in the population.