Drawing from work on the meta-analysis of over 500 validation studies of the General Aptitude Test Battery (GATB) by the U.S. Employment Service, the paper presents a methodological message and a substantive message. Gene Glass's methods, as used by Edwin Ghiselli in personnel selection, ignore study artifacts (sampling error, error of measurement, and range restriction) and lead to a misinterpretation of effect size across studies. Therefore, conclusions on the low predictive power of cognitive testing and the need for local validation are false. Meta analysis has dramatically altered the knowledge from personnel selection studies. Validity (Tables 1 and 2) show that general cognitive ability predicts performance in every job, and better than other pretraining predictors (Table 3). Current job performance predicts future job performance as well as ability (Table 4). While general cognitive ability predicts job performance primarily because it correlates highly with job knowledge, the beta weight indicates ability is also directly related to performance. A detailed, five-page topic outline is appended. (BS)