To do so, we will needs first to consider metthodological techniques used by psychologists when reviewing existing literature.Three major kinds of techniques have been used. The first,narrative review,involves locating and reading as many sources as one can and then writing up one's conclusions. Although such summaries can be useful, Hyde and Linn pointed out that the narrative review has several shortcomings:"It is non quantitative, unsystematic,and subjective, and the task of reviewing 100 or more studies.