HOW MANY CAUSES ARE THERE OF AGING-RELATED DECREMENTS IN COGNITIVE-FUNCTIONING

Two analytical methods are proposed to evaluate the extent to which th e age-related influences in a set of variables are independent of one another. Application of the methods to 16 different data sets, represe nting a total of 169 variables and 4505 subjects, reveals that as few as one or two distinct factors may be sufficient to account for a larg e proportion of the age-related variance in a variety of cognitive var iables. These results therefore imply that a relatively small number o f independent ''causes'' may be responsible for a substantial percenta ge of the age-related declines apparent in many measures of cognitive functioning. (C) 1994 Academic Press, Inc.