International Journal of Epidemiology, Vol 26, 1097-1106, Copyright © 1997 by International Epidemiological Association
GH Maude and DA Ross
BACKGROUND: Verbal autopsies (VA) are increasingly being used in developing
countries to determine causes of death, but little attention is generally
given to the misclassification effects of the VA. This paper considers the
effect of misclassification on the estimation of differences in
cause-specific mortality rates between two populations. METHODS: The bias
in the percentage difference in cause-specific mortality between two
populations has been explored under two different models: i) assuming that
mortality from all other causes does not differ between the two
populations; ii) allowing for a difference in mortality from all other
causes. The bias is described in terms of the sensitivity and specificity
of the VA diagnosis and the proportion of mortality due to the cause of
interest. Methods for adjustment of sample size and adjusting the estimate
of effect are also explored. RESULTS: The results are illustrated for a
range of plausible values for these parameters. The bias is more extreme as
both sensitivity and specificity fall, and is particularly affected even by
a small loss of specificity. The bias also increases as the proportion of
all deaths due to the cause of interest decreases, and is affected by the
size of the true change in mortality due to the cause of interest relative
to the change in mortality from other causes. Calculations from existing
data suggest prohibitively large sample sizes may often be required to
detect important differences in cause-specific mortality rates in studies
using existing VA. CONCLUSIONS: Highly specific VA tools are needed before
observed differences in cause-specific mortality can be interpreted. Loss
of power due to misclassification may obscure real differences in
cause-specific mortality.
ARTICLES
The effect of different sensitivity, specificity and cause-specific mortality fractions on the estimation of differences in cause-specific mortality rates in children from studies using verbal autopsies
Tropical Health Epidemiology Unit, London School of Hygiene and Tropical Medicine, UK.
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