OBJECTIVE: To measure cognitive change using a brief measure over a period
of 9 years and to adjust for attrition in the sample.
DESIGN: The Cambridge City over 75 Cohort (CC75C), a complete sample of the
75 years and older age group from five group general practices in the city
of Cambridge with a systematic one-third of a further practice, all follow
ed on four occasions.
SETTING: Cambridge city, UK, the respondents' place of residence.
PARTICIPANTS: A total of 2106 subjects were included at study entry.
MEASUREMENTS: A brief interview, administered by a trained interviewer, con
taining a short cognitive scale and the Mini-Mental State Examination (MMSE
) at baseline, 2.4 years, 6 years, and 9 years.
RESULTS: Decline in MMSE scores occurred across the population and was grea
ter in the oldest age groups. Attrition at later stages of the follow-up wa
s associated with greater decline at earlier stages. Adjusting the results
for loss to the sample leads to considerably higher estimates of decline, w
ith the older age groups declining faster from lower levels.
CONCLUSIONS: To date, cognitive decline in the very old has been considerab
ly underestimated by longitudinal studies. If studies of population samples
are to reflect the health and social needs of this frail group accurately,
adjustments for the effect of attrition must be included before true decli
ne can be estimated.