Estimating incidence of dementia subtypes: assessing the impact of missed cases

Ascertaining dementia-related outcomes for deceased or proxy-dependent participants: an overview of the Women's Health Initiative Memory Study supplemental case ascertainment protocol

OBJECTIVE

The aim of the study was to compare a two-staged clinic-based standardized protocol with a supplemental proxy-based protocol.

METHODS

The Women's Health Initiative Memory Study enrolled 7479 women, aged 65-79 years and free of dementia, in a clinical trial of postmenopausal hormone therapy who were followed for up to 13 years with annual two-staged clinic-based standardized protocols to identify incidence of probable dementia. A supplemental proxy-based protocol, involving telephone administration of the dementia questionnaire, was designed to assess the cognitive status of women who could no longer attend clinic visits because they died (n = 1058) or became dependent (n = 228). Chi-squared tests were used to compare characteristics of women eligible for proxy-based versus clinic-based assessment. Risk factor relationships were described using proportional hazards regression.

RESULTS

Women who were eligible for proxy-based assessments tended to have worse cognitive impairment risk factor profiles and had higher rates of probable dementia (15.2% vs 3.5%) than clinic-assessed participants. Augmenting the clinic-based cases with those identified from proxy interviews reduced undercounting and materially altered observed relationships that years since menopause, smoking status, diabetes, and prior use of hormone therapy had with incidence of probable dementia.

CONCLUSIONS

Although proxy interviews were successful in reducing biases in estimated incidence rates and risk factor relationships, it is unlikely that they will fully eliminate many biases. Proxy-based assessments are necessary in longer term studies to reduce undercounting of dementia cases and to characterize risk factor relationships.

Changing patterns of adult (45–74 years) neurological deaths in the major Western world countries 1979–1997

OBJECTIVES

To compare changes in 'adult' (45-74 years) 'all-cause deaths' (ACDs) with all neurological death categories by age and gender in the 10 major Western countries between the 1970s (1979-1981) and the 1990s (1995-1997).

METHOD

World Health Organization standardized mortality data for age and gender (1979/97) were used to examine changes in adult mortality rates per million based upon ICD-9 categories for ACDs, 'neurological deaths' and the special neurological categories of 'other neurological deaths' (ONDs) and 'mental disorder deaths' (MDDs), which include the dementias. Ratios of ratios were calculated to demonstrate how each individual country's pattern changed over the period by age and gender, resolving the problem of cross-national comparisons. Rates of change across the endpoints and between age groups (45-54, 55-64, 65-74 and 75+ years) were examined using analysis of variance, stepwise regression analysis and cross-tabulation analyses.

RESULTS

Meningitis deaths fell substantially, but there was little change in multiple sclerosis or epilepsy deaths. OND rates for the 1990s increased compared with the 1970s rates for males and female, in actual terms and relative to ACDs for almost all countries. Many of the relative rates of increase were substantially higher than 20%. There were significant statistical differences with respect to relative rates of ONDs between the 1970s and the 1990s data, even when the 75+ years age group was excluded. Significant differences were also found between age groups, but only in the 1990s data. MDD rates showed similar trends. Analyses of actual rates of increase in these causes of death showed that males outnumber females in all ages below 74 years. The extent of this difference remained constant across the endpoints. However, in those aged 75 years and over, females outnumbered males at both endpoints, but this disparity widened significantly in the 1990s data.

CONCLUSIONS

The 1990s data indicate substantial increases compared with the 1970s data for ONDs (especially amongst 65-74 year olds), and rises in MDDs in 55-64 year olds in five countries, including England and Wales and Germany, and in 65-74 year olds in most countries, suggesting earlier onsets of the underlying conditions. Further country-specific research is required to explain the emerging morbidity and mortality.