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There is a widespread belief, particularly among elderly people, that activity prevents cognitive decline in old age and protects against the onset of dementia. This view is reflected in the philosophy of many organizations, such as the University of the Third Age , which claim that mental activity is crucial in preventing cognitive impairment. The importance of an active lifestyle has also received support within the scientific community [2-6]. A recent editorial in the British Medical Journal  stated that `stimulating mental activity is worthwhile' (p. 952) in protecting against dementia and called for further experimental investigation of the issue.
The present study investigated the role of activity on cognitive performance in a large community sample of elderly subjects. The primary aim was to determine whether differences in cognitive performance could be accounted for by activity, particularly when the influence of other variables, such as sex, sensory functioning , health , education  and disability were taken into account. These variables have been found previously to be predictive of cognitive performance. A secondary aim was to examine whether age continued to be predictive of cognitive performance once account had been taken of activity, health, education, sex, disability and sensory functioning. This allowed investigation of the hypothesis that activity and other variables account for age-associated changes in cognitive functioning. This hypothesis predicts that once the effects of activity are accounted for, no further age effects should be present. A third aim was to examine the hypothesis that activity was more influential in older than younger subjects. Christensen and Mackinnon  and Hultsch et al.  noted that maintaining high levels of activity may be of greater importance in very elderly subjects than in younger elderly people. Furthermore, because earlier findings suggested that activity levels were not independent of education, and that activity may offset to some degree education disadvantage [10, 11], the interactions between activity and education were also examined.
The sample: The subjects were a sample of elderly persons living in the community in the Australian city of Canberra and adjacent town of Queanbeyan Elderly people were sampled from the electoral roll which is a register of eligible voters. Registration on the electoral roll is compulsory for all Australian citizens aged 18 or more. The sample was drawn at random within three age strata to give an equal achieved sample of men and women. For each sex, there were three age strata (70-74 years, 75-79 and more than or equal to 80 years), with each stratum sampled to give an achieved sample which was proportional to the number of individuals in the population at that age group.
The persons sampled were sent a letter inviting participation in the survey and then approached at home by trained interviewers. The purposes of the study and what was asked of the participant were explained orally. If a person was unable to give informed consent owing to disability, the principal caring relative was asked. If an interview was granted, the subject was asked at the end to nominate a close relative or friend who knew him/her well and would be able to describe his/her present circumstances. An interview was then sought from the informant nominated. Thirty-one per cent of those approached refused to participate. This refusal rate is similar to those recently obtained in other community samples. Sixty-five per cent of refusers were women, but the age range of the refusers did not differ from that of the participants. The sample used in the present paper consisted of 858 subjects aged 70-89 years of age who completed data on the self-activity scales, the Mini-Mental State Examination (MMSE)  and sensory functioning. Of these, 664 subjects had informant data available. Subjects were divided into four age groups, 70-74, 75-79, 80-84 and 85-89 years.
General procedure: Subjects were interviewed in their own homes by trained interviewers. Information necessary for the diagnosis of dementia and depression was collected, as well as information on social background, personality, social support, self-reported cognitive function and the use of services. Prevalence rates for depression and dementia have been reported elsewhere, as have data on health, neuroticism and cognitive functioning [13-18].
Measures of inactivity: Both informants and subjects were asked about how often `these days' the subject read a newspaper, engaged in physical activity (such as sport, walking, heavy gardening, cleaning), was involved in interests and hobbies, spent time sitting around without doing very much (e.g. resting, dozing, watching the TV without caring what the programme was), spent time in planned activities, and had a daily nap. Each of these activities was rated on a scale with from 2 to 4 points. For example, subjects were asked `How often do you read a newspaper, book or magazine these days?' (0 = every day, 1 = most days, 2 = once a week, 3 = less than once a week). The six items were combined to form a scale. Five items had 4 points and one item had 2 points, making 16 the maximum score for the scale. Scores were pro-rated if up to three of the six items were completed. If fewer than three items were completed, the scale was listed as missing. Informants' reports were summed in the same manner to give scores from 0 to 16, with higher scores indicating greater inactivity. The correlation between informant and subject total scores on the activity measures was 0.74 (n = 664), showing strong agreement. Cronbach alpha for the self-report scale was 0.64 (n = 841) and for the informant scale was 0.69 (n = 603).
Because the items on the scale measured a variety of physical, social and mental activities, the scales were subjected to principal …