Department of Psychological Medicine, University of Sydney, Rozelle Hospital, Rozelle, NSW 2039, Australia
Korten & Henderson (2000) described findings from a 1997 national survey, in which a "household sample of 10 641 individuals representative of the adult population of Australia" was interviewed. They reported that "the prevalence of a diagnosis of any ICD-10 anxiety or depressive disorder... declines for both men and women after the age of 55 years", and noted a trend for psychological symptoms to be fewer among the older age groups. Before accepting the findings as evidence that depression is less prevalent in old age (a conclusion that might affect decisions about allocation of resources), the following points should be noted (see Snowdon et al, 1998).
First, the (approximately) 1600 subjects aged over 65 years were not truly representative of the older population. The survey excluded the 10% of older Australians who were temporarily or permanently residing in institutes (e.g. hospitals, nursing homes, boarding houses), or homeless at the time of the survey. It also excluded those with moderate or severe dementia (Mini-Mental State Examination score <18). The prevalence of depression is considerably higher among those with physical disability, those in residential care and those with dementia.
Second, the instrument forming the core of the interview was the automated version of the Composite International Diagnostic Interview (CIDI), which discounts symptoms attributable to physical illness (Jorm, 2000). Studies that rely on subject-reported symptoms may underestimate the severity of depression in old age, since older patients with depression are less likely than younger patients to acknowledge having affective symptoms (Lyness et al, 1995).
Third, the response rate in this survey was 78%, but the response rate of different age-groups was not known. In other surveys (e.g. Kramer et al, 1985), older subjects have been twice as likely as younger adults to decline involvement. Refusers are more likely to be depressed.
Finally, the report did not differentiate prevalence rates in young-old and old-old individuals, yet various researchers have found a progressive increase in rate from 55 to 85 years. Jorm (2000) commented on the lack of consistency between researchers regarding whether or not depression becomes less prevalent in old age.
REFERENCES
Jorm, A. F. (2000) Does old age reduce the risk of anxiety and depression? A review of epidemiological studies across the adult life span. Psychological Medicine, 30, 11-22.[CrossRef][Medline]
Korten, A. & Henderson, S. (2000) The
Australian National Survey of Mental Health and Well-Being. Common
psychological symptoms and disablement. British Journal of
Psychiatry, 177,
325-330.
Kramer, M., German, P. S., Anthony, J. C., et al (1985) Patterns of mental disorders among the elderly residents of Eastern Baltimore. Journal of the American Geriatrics Society, 33, 236-245.[Medline]
Lyness, J. M., Cox, C., Curry, J., et al (1995) Older age and the underreporting of depressive symptoms. Journal of the American Geriatrics Society, 43, 216-221.[Medline]
Snowdon, J., Draper, B., Chiu, E., et al (1998) Surveys of mental health and wellbeing: critical comments. Australasian Psychiatry, 6, 246-247.
Centre for Mental Health Research, The Australian National University, Canberra, ACT 0200, Australia
Professor Snowdon questions the validity of the results on the elderly from the Australian National Survey of Mental Health and Well-Being. He rightly points out that the survey failed adequately to cover the population living in institutional care, which was 9% of Australians over 65 in 1998. This is clearly acknowledged in earlier publications. Indeed, the indigenous people of Australia, people in prison, the homeless, the armed forces and the migrant population were also not included in numbers large enough to give stable prevalence estimates, mainly for the sake of economy in what was already a very large undertaking. We used "an unweighted sample with no group represented in a proportion greater than its frequency in the population" (Henderson et al, 2000).
The lack of information concerning the 22% non-responders is indeed regrettable, but does not detract from the finding, consistent with many of the studies cited in Jorm (2000), that the community-dwelling elderly displayed significantly lower levels of depressive symptomatology than younger cohorts. This was reflected in the prevalence rates and in all the scales of psychological distress measured in the survey: the 12-item General Health Questionnaire (GHQ-12), the 12-item Short-Form General Health Survey (SF-12), the Kessler-10 scale, the CIDI screen items for depression and finally the neuroticism items from the Eysenck personality questionnaire considered to reflect vulnerability to psychological symptoms. Each of these scales handles symptoms associated with physical disability in a different way. In all cases, the lower levels of symptomatology observed among 65-to 70-year-olds were maintained into the oldest age group (75 years and above), although the pattern is less stable than for younger age groups because of smaller numbers. The interested reader is referred to Jorm (2000) for a discussion of the possible mechanisms involved.
Information on mental disorders among the oldest old and institutional elderly are of crucial importance for advocacy. But this needs to be addressed in ways other than in large community surveys. This was made explicit from the beginning, where we stated that information on "some of the most significant elements in our society" would need special studies (Henderson et al, 2000). Any concern that our findings might affect decisions about allocation of resources is unlikely to be justified, because it assumes that administrators and policy-makers will make the grave error of extrapolating from community estimates to the special population of the elderly in hostels and nursing homes.
REFERENCES
Henderson, S., Andrews, G. & Hall, W. (2000) Australia's mental health: an overview of the General Population Survey. Australian and New Zealand Journal of Psychiatry, 34, 197-205.[CrossRef][Medline]
Jorm, A. F. (2000) Does old age reduce the risk of anxiety and depression? A review of epidemiological studies across the adult life span. Psychological Medicine, 30, 11-22.[CrossRef][Medline]
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