DOES IT ALL GO TOGETHER WHEN IT GOES - THE 19TH BARTLETT MEMORIAL LECTURE

As groups of people age, the differences in the cognitive abilities of the most and least able become more extreme. This increase in between -individual variance is accompanied by an increase in within-individua l variance: the difference between individuals' levels of performance on their best and least well retained skills. The implications of incr easing between-individual variance are discussed in terms of the range of different factors that may affect cognitive ageing. Increases in w ithin-individual variance are discussed in terms of differences betwee n ''fluid'' and ''crystallized'' abilities. The usefulness of this dis tinction and its functional implications are questioned. The hypothesi s that age-related declines in ''fluid'' abilities are best modelled i n terms of declines in a single factor is evaluated. Evidence is prese nted of disparate rates of decline, even of ''fluid'' cognitive abilit ies, such as performance on IQ tests, ability on information-processin g tasks, and efficiency on memory tasks. Data from large-scale cross-s ectional studies suggests that cognitive skills do not ''all go togeth er when they go'', but that there may, rather, be characteristic patte rns, or syndromes, of cognitive ageing.