Estimating surgical volume--outcome relationships applying survival models: accounting for frailty and hospital fixed effects.

This paper investigates the surgical volume-outcome relationship for patients undergoing hip fracture surgery in Quebec between 1991 and 1993. Using a duration model with multiple destinations which accounts for observed and unobserved (by the researcher) patient characteristics, our initial estimates show that higher surgical volume is associated with a higher conditional probability of live discharge from the hospital. However, these results reflect differences between hospitals rather than differences within hospitals over time: when we also control for differences between hospitals that are fixed over time, hospitals performing more surgeries in period t + 1 than in period t experience no significant change in outcomes, as would be predicted by the 'practice makes perfect' hypothesis. The volume-outcome relationship for hip fracture patients thus appears to reflect quality differences between high and low volume hospitals.