For longitudinal research, how can correlations be computed between scores obtained on the ages 18-59 forms and scores obtained later on the older adult forms?

Answer: Correlational and regression statistics are not affected by the absolute magnitudes of the scores at each assessment point. Consequently, they can be used to compute longitudinal associations between the raw scores or T scores obtained from each instrument. For adaptive functioning scales, syndrome scales, DSM-oriented scales, and the Critical Items scale, raw scores provide more differentiated analyses than T scores do, because the T scores are truncated. To provide a more precise measure of longitudinal associations between the corresponding sets of items on the ages 18-59 forms and older adult forms, users can compute correlations between the sum of scores for the ASR items that have counterparts on the OASR. Likewise, users can compute correlations between the sum of scores for the items that have counterparts on the ABCL and OABCL