The prevalence of coffee drinking among hospitalized and population-based control groups
D. T. Silverman, R. N. Hoover, G. M. Swanson and P. Hartge
Data on coffee-drinking habits obtained from a case-control study conducted
in Detroit were used to compare the proportions of coffee drinkers in a
hospital and a population control series. The comparison was based on
interviews with 262 hospitalized controls and 427 population controls. The
overall proportion of coffee drinkers in the total hospital control group
was similar to that in the population control group. However, the
proportion of moderate-to-heavy coffee drinkers among controls hospitalized
for conditions that may have caused them to alter their diet (eg,
gastrointestinal disorders and cardiovascular disease) was lower than that
among population controls. In contrast, the proportion of moderate-to-heavy
coffee drinkers among controls hospitalized for conditions that probably
did not cause a change in diet (eg, fractures) was almost identical to that
among population controls. These results suggest that, in hospital-based
case-control studies of the effects of coffee consumption, it would be
prudent to restrict the referent group to those patients hospitalized for
conditions that probably did not cause a change in diet. The magnitude of
bias resulting from failure to exclude controls hospitalized for
diet-altering conditions will depend on two factors that may vary between
studies: (1) the distribution of diet-altering conditions among the
hospital controls, and (2) the relationship of these diseases to coffee
consumption.
