The research also sought to determine whether the validity differed for black and white youth. Data in the Pittsburgh Youth Study were collected from 3 samples of about 500 youths each; they were initially studied in the 1st, 4th, and 7th grades. The first two data collection waves produced delinquency seriousness scores for the middle sample up to an average age of 10.7 years and for the oldest sample up to an average age of 13.9 years. In addition, Allegheny County (Pa.) juvenile court records were examined for offenses committed by each youth between his 10th and 18th birthdays, covering the period before and up to 6 years after the assessments. Results revealed that concurrent validity was higher than predictive validity, possibly because juvenile court petitions increased the willingness of youths to report their delinquent acts. The combined scale had similar concurrent validity but greater predictive validity than the self-report scale; the combined scale also identified a greater number of youths as serious delinquents. Concurrent validity for admitting offenses was higher for white youths, but concurrent validity for admitting arrests was higher for black youths. No consistent racial differences existed in predictive validity. Findings indicated that predictive validity increases by combining self-report data with information other sources. Findings also indicated that, in the Pittsburgh Youth Study, the ethnic differences in official delinquency were partly attributable to ethnic differences in delinquent behavior and were not attributable to differential ethnic attrition or differential ethnic validity of measures of delinquent behavior. Tables, footnotes, and 46 references (Author abstract modified)