The proposed study will extend the investigation of short-term longitudinal methodologies for the study of adult cognitive behavior. Special emphasis will be given to the identification of environmental correlates of change in intellectual functions, and the effects of experimental mortality and test-retest effects will be analyzed for successive cohorts and times of measurement. A cross-sectional sample of 500 Ss covering the age range from 22 to 70 years which was studied in 1956 and retested in 1963 and 1970 will be re-examined after another seven year interval. A second sample of 960 Ss first tested in 1963 and retested in 1970, and a third sample of 701 Ss first tested in 1970, will also be re-examined. A new random sample of approximately 700 Ss will be drawn from the same parent population. Measures used in the past and to be repeated include Thurstone's Primary Mental Abilities Test and Schaie's Test of Behavioral Rigidity. In addition, health history, personality and descriptions of individual environments will be collected. Health history data for the entire fourteen year period is available on all Ss (who are members of a prepaid medical plan) and will be related to concurrent intellectual status and change in cognitive function. Convergent studies will be made to check on the effect of switching from a sampling without replacement to one with replacement basis and on the effect of switching to newer forms of the PMA Test. A battery will be developed to describe individual micro-environments, data from which will be related to change in cognitive function.