riod of growth but show little or no decline. Vocabulary , for example,
tends to grow dramatically in childhood and then to level out after theend of formal education, with little change thereafter.
These trends do not exhaust the possibilities. Perhaps growth in
personality is unlimited, like the physical growth of some fish. Perhapsthe pattern of change is not a simple up or down but a complicated pat -
tern of peaks and troughs—a possibility suggested by some of the stage
theories we have mentioned. Rather than belabor the possible, let usturn to the facts and see if we can simply describe the age trends in per -
sonality dimensions. Later we can worry about what they mean or
where they come from.
CROSS-SECTIONAL STUDIES
OF PERSONALITY DIFFERENCES
There are some fairly obvious ways of going about looking for this kind
of age trend. First, we can measure an individual’s personality now , andthen return in 10, or 20, or 40 years to measure it again. We could thentell what net change, if any , had occurred in the meantime for each indi-vidual. This is a longitudinal design, in many respects the best way tostudy aging. The major problem with longitudinal studies is quite sim-ple: They take too long. Few scientists are willing to wait 10 years forresults, let alone 40. Gardeners may be willing to plant trees now thatwill not bear fruit for 10 years, but few researchers see themselves asgardeners. In fairness, there are some differences. Gardeners know thatif they wait patiently they will be rewarded with apples or cherries orplums. Researchers never know what they will find out, or if the resultswill turn out to be interesting or informative. If they knew the answers,they would not need to ask the questions.
What one really wants is some shortcut method of answering the
question of age changes, and the cross-sectional method is invaluable asthat kind of tool. In cross-sectional designs, one takes a group of youn -
ger people and a group of older people and compares them on the traits
of interest. We might observe that 40% of men over 60 were baldwhereas only 2% of men under 30 were. Hence, it would seem, baldnessis age related. This is an example of the kind of cross-sectional observa -
tion we all make, and it is almost certainly a correct conclusion.
Studies that compare groups of different ages are called cross-Growth or Decline in Personality 59