Personality variation and age: trait instability or measurement unreliability?

There is controversy over the lifelong nature or otherwise of personality traits, non-stability being accounted for by the underlying trait varying or by psychometric properties of the questionnaire used. The evidence suggests traits are less stable in younger adults than older adults. This study aims to verify this finding using a large population-based cohort study. The Health and Lifestyle Survey measured the personality of 2997 individuals in both 1984 and 1991. The Spearman's Rho and Cronbach's Alpha were calculated for each year-of-age band. Rank order stability of Neuroticism and Extraversion increased with age and there was no effect of age on Alpha score. This finding supports the notion that it is the underlying traits that are less stable in the young rather than the instrument having poor psychometric properties in younger people.