they should worry about practice effects or whether they can safely ig -
nore them.)
This design, in which different individuals born at the same time
are measured at two or more different times, is known as a “cross-se -
quential design with independent samples,” or, as we will call it, a cross-
sequential design. Douglas and Arenberg (1978) reported cross-sequen -
tial analyses on the GZTS scales. Their two samples were collected at
successive intervals (1958–1968 and 1968–1974), making this kind ofanalysis possible. Their second sample scored lower than their first onEmotional Stability , Personal Relations, and Masculinity , suggesting anincrease in Neuroticism. Note that this finding appears to contradict thesmall cross-sectional decline in Neuroticism shown in Figure 2. None ofthe other GZTS scales showed significant cross-sequential effects.
A related approach is called a time-sequential design : Here individu -
als of the same age are measured at different times: 60-year-olds, for ex-
ample, might be surveyed in 1980 and in 2000. The differences couldnot be caused by aging itself, since both groups are the same age. Theycould, however, be the result of generational differences, since the 60-year-olds of 1980 were born in 1920 whereas the 60-year-olds of 2000were born in 1940. A great deal of ingenuity went into the invention ofthese designs, and they elegantly solve some of the vexing problems ofaging research. But they too are ambiguous, for a reason that has not yetbeen mentioned.
Take as an example attitudes toward women. Suppose we had
asked a national sample of 20-year-olds in 1960 if they believed thatwomen should have their own career, freedom of choice in family plan -
ning, or the right to participate in professional sports. Relatively few
would have endorsed these aspirations. But if we had asked the samequestions of a different group from the same cohort (now 60-year-olds)in 2000, presumably a much larger proportion would have agreed(Costa & McCrae, 1982). We know this is not a cohort effect, or gener -
ational difference, since all these individuals were born in the same
year. We know it is not a practice effect, since the respondents in oursecond sample have never been interviewed before. But surely wewould not conclude that it was an aging effect, that individuals adoptincreasingly liberal attitudes toward women as they grow older. It ismore likely that we would insist the times had changed and almost ev -
eryone had modified opinions on these issues as a result of the Women’s
Movement. This would be a clear example of what is known as a time-
of-measurement effect .Growth or Decline in Personality 73