Mortality Risks and Classification Issues
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Data on the degree to which various age-related conditions contribute to mortality is actually a lot less precise than most people assume it to be. Cause of death in old age is often either ambiguous or ambiguously recorded, leading to the need for estimation and correction via statistical methods. This opens the door to arguments as to the plausibility of data for any particular age-related condition, claiming that it is either more or less of a threat than previously thought. Here, for example, epidemiologists argue that Alzheimer's disease causes far more deaths than are officially reported as being due to this condition:

Data came from 2,566 persons aged 65 years and older (mean 78.1 years) without dementia at baseline from 2 cohort studies of aging with identical annual diagnostic assessments of dementia. Because both studies require organ donation, ascertainment of mortality was complete and dates of death accurate. Mortality hazard ratios after incident AD dementia were estimated per 10-year age strata from proportional hazards models. Population attributable risk percentage was derived to estimate excess mortality after a diagnosis of AD dementia. The number of excess deaths attributable to AD dementia in the United States was then estimated.

Over an average of 8 years, 559 participants (21.8%) without dementia at baseline developed AD dementia and 1,090 (42.4%) died. Median time from AD dementia diagnosis to death was 3.8 years. The mortality hazard ratio for AD dementia was 4.30 for ages 75-84 years and 2.77 for ages 85 years and older (too few deaths after AD dementia in ages 65-74 were available to estimate hazard ratio). Population attributable risk percentage was 37.0% for ages 75-84 and 35.8% for ages 85 and older. An estimated 503,400 deaths in Americans aged 75 years and older were attributable to AD dementia in 2010.

[Thus] a larger number of deaths are attributable to AD dementia in the United States each year than the number (less than 84,000 in 2010) reported on death certificates.

Given that there were overall 2.5 million deaths in the US in 2010, with the largest attributed causes being cancer and heart disease, this paper is suggesting that a large systematic miscategorization exists, not just the need for a modest correction.

Link: http://dx.doi.org/10.1212/WNL.0000000000000240

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