In the present study a large sample of credible patients (n = 172) scored significantly higher than a large sample of noncredible participants (n = 195) on several WAIS-III Picture Completion variables: Age Adjusted Scaled Score, raw score, a "Rarely Missed" index (the nine items least often missed by credible participants), a "Rarely Correct" index (nine items correct <26% of the time in noncredible participants and with at least a 25 percentage-point lower endorsement rate as compared to credible participants), and a "Most Discrepant" index (the six items that were the most discrepant in correct endorsement between groups-at least a 40 percentage point difference). Comparison of the various scores showed that the "Most Discrepant" index outperformed all the others in identifying response bias (nearly 65% sensitivity at 92.8% specificity as compared to at most 59% sensitivity for the other scores). While no differences in Picture Completion scores were observed between less-educated (<12 years) and better-educated (≥12 years) credible participants, noncredible participants with <12 years of education scored significantly poorer than noncredible participants with 12 or more years of education. On the "Most Discrepant" index, 76.7% of less-educated noncredible participants were detected as compared to 58.3% of better-educated noncredible participants. Results of the current study suggest that the Picture Completion subtest of the WAIS-III is an effective measure of response bias, and that it may have a unique role in identifying suboptimal effort in less-educated test takers.