Pollsters are as plagued by time-of-measurement problems as edu -
cators are by practice effects. Some theorists (P . B. Baltes & Nesselroade,
1972) have claimed that these problems are less crucial to personalityinvestigators because personality is unlikely to be shifted by temporaryhistorical movements or swings in attitude. Perhaps so, perhaps not. Inview of how little we know about adult personality , many would arguethat it is not safe to make that assumption. What we need is a designthat avoids the problems of the cross-sequential design—one that cancompare people at different ages but in which we can rule out the possi -
bility that time of measurement is responsible for the apparent effect. Is
there any way to do this?
There is one way . We can eliminate time-of-measurement effects
(and practice effects) if we measure all our subjects only once, all at onetime. Of course, in order to see the effects of age, we would have tomeasure simultaneously individuals of different age groups. And this, loand behold, is nothing other than the cross-sectional design with whichwe started. We have come full circle.
This curious circumambulation has bedeviled researchers for years
and left the field in some perplexity . A number of additional designs ofgreater complexity have been proposed to break out of the circle, butcritics have always been able to weave them back in. The fact is thatindividuals are always born in one and only one generation, and theyalways grow older during a certain historical period when things arechanging in a certain way and to a certain degree. Short of cloning peo-ple to raise them in different circumstances, we find no way out of thedilemma. Time, cohort, and aging are inextricably confounded.
AN INTEGRATED APPROACH
We might at this point abandon all hope and move to another field ofstudy . Alternatively , we can adopt a more constructive point of view(Costa & McCrae, 1982). Although there is no way to be sure that weinterpret an effect correctly , there are ways to improve our chances. Forexample, when we see the same direction and magnitude of an effect incross-sectional, cross-sequential, and longitudinal studies, it becomeshighly likely that a real aging effect has been found. Exactly this patternwas found when analyses of health problems were conducted (Costa &McCrae, 1980b). All types of analyses pointed to an increased frequency74 PERSONALITY IN ADULTHOOD