1987) and quickly became advocates of the FFM. We developed scales
to measure Agreeableness and Conscientiousness to supplement ouroriginal instrument and published it as the NEO Personality Inventory ,or NEO-PI (Costa & McCrae, 1985, 1989a).
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If the FFM is a truly comprehensive taxonomy of personality traits, it
has profound implications for the study of aging and personality . Thetask of looking for age changes, for example, is immensely simplified.Instead of being obliged to consider separately each of the 18,000 traitsnamed in the English language and the hundreds of scales created bypsychologists, we can concentrate on five broad groups of traits. Bysampling traits from each domain, we can get a reasonable idea of howall traits are related to age.
To the extent that existing measures can be classified in terms of a
taxonomy , the FFM can be used to summarize the existing literatureand to look for similar patterns across different instruments. Further,the comprehensiveness of the model would ensure that our search forage changes was exhaustive. We would not need to worry that we hadinadvertently overlooked some trait that shows striking age changes. Ifwe see maturation in some traits in a domain, we may wish to look care-fully for changes in other traits in the same domain. Studies of aging of-ten require decades of data collection, so researchers need to be very se-lective in the variables they choose to study . The FFM can help usformulate plausible hypotheses about which traits must be representedand which can be safely ignored.
But the FFM has many other applications in the psychology of ag -
ing because it provides a framework for systematic research. Whether
we are interested in the so-called midlife crisis, preferred age of retire -
ment, adjustment to widowhood, or risk factors for dementia, we know
we have fully considered the possible role of personality if and only ifwe have measured all five factors.
But is the claim to comprehensiveness justified? Does the FFM in
fact encompass all the competing systems? This is an empirical ques -
tion, and we must postpone our answer until we have considered how
personality traits should be measured.36 PERSONALITY IN ADULTHOOD