Varied definitions of hospital volume did not alter the conclusions of volume-outcome analyses

Objective — To compare different methods of calculating hospital volume, including approaches designed to account for hospital restructuring, and their impact on volume-outcome analyses.

Study Design and Setting — Using a population-based cohort of acute myocardial infarction (AMI) patients hospitalized between 1992 and 2004 in Ontario, Canada, we assessed the association between hospital volume and 30-day mortality using four different volume definitions. Bootstrapping was used to compare the odds ratios (ORs) of the different volume definitions.

Results — All four of the volume definitions tested resulted in statistically significant volume-outcome analyses. Using external data to account for hospital restructuring did not alter the conclusions of volume-outcome analyses. Nevertheless, statistically significant heterogeneity in the magnitude of the estimated ORs for the volume-outcome relationship was observed across the different volume measurement methods.

Conclusions — The conclusions of hospital volume-outcome analyses are similar regardless of how hospital volume is defined. However, the heterogeneity in the volume ORs suggests that direct policy application of these ORs requires the most accurate method of defining volume.