Estimates of the trend of lethality over time usually suggest that it has declined.
Sometimes it is said that the declining case fatality rate of diseases and injuries has
matched the declining death rate. Yet in the last 150 years causes of sickness and death
have shifted in a major way. These shifts are usually referred to as the epidemiologic
transition, which acknowledges a transition from infectious diseases to respiratory
diseases to organ diseases and to degenerative diseases.
With support from the National Institutes of Health, I have accumulated data sets that
make it possible to reconstruct changes in the lethality of diseases and injuries over
time while controlling for age, gender, and specific diseases. I have previously given
preliminary versions of this paper, using partial data sets from Australia. In this paper
I propose to present findings from the complete data sets, which include some 25,000
episodes of sickness in Australia and Great Britain. The partial data sets suggest that
the lethality of communicable diseases declined while the lethality of noncommunicable
diseases rose. Overall there was, until the 1950s, little change in the likelihood that an
episode of sickness serious enough to oblige someone to take off from work would end in
recovery.
If these findings hold up in analysis of the complete data sets they have important
implications for health demography. The persistence of higher levels of disease lethality
helps explain why age-specific sickness rates did not decline during the health
transition. That persistence also suggests that survival to higher ages was accompanied by
exposure to diseases that remained intractable. Thus the decline of mortality from
communicable diseases, which allowed people to live to higher ages, led to longer sickness
episodes and more often lethal episodes at higher ages. The latest findings from health
surveys indicate that age-specific sickness rates in the 1990s remain high, even though
lethality appears to have begun to diminish.
