The National Halothane Study was designed to examine the possible association of halothane anesthesia and postoperative massive hepatic necrosis. It was a retrospective survey of the incidence of fatal massive hepatic necrosis and overall death rate following general anesthesia in 34 hospitals for the four-year period from 1959 through 1962. A summary of the observed incidences of liver necrosis and mortality following halothane anesthesia and following use of other general anesthetic agents has been published in The Journal.1 One important by-product of the study was the finding of large differences in postoperative mortality occurring among the participating institutions. The following communication represents a summary of the statistical analysis of these institutional differences and a discussion of their possible significance.
Death rates for the six-week period following surgery varied widely among the 34 institutions cooperating in this study. These death rates ranged from 0.27% to 6.40%, a 24-fold ratio. In