Definition and adjustment of Cesarean section rates and assessments of hospital performance.

Background. Demand is growing for comparative data such as Cesarean section rates, but little effort has been made to develop either standardized definitions or risk adjustment approaches. Objective. To determine to what extent a seemingly straightforward indicator like Cesarean section rate will vary when calculated according to differing definitions used by various performance measurement systems. Design. Retrospective data abstraction of 200 deliveries per hospital. Setting. Fifteen acute care hospitals including two from outside the USA. Measurements. Four widely-used performance measurement systems provided specifications for their Cesarean section indicators. Indicator specifications varied on inclusion criteria (whether the population was defined using Diagnostic Related Groups or ICD-9-CM procedure codes or ICD-9-CM diagnosis codes) and risk-adjustment methods and factors. Rates and rankings were compared across hospitals using different Cesarean section indicator definitions and indicators with and without risk adjustment. Results. Calculated Cesarean section rates changed substantially depending on how the numerator and denominator cases were identified. Relative performance based on Cesarean section rankings is affected less by differing indicator definitions than by whether and how risk adjustment is performed. Conclusions. Judgments about organizational performance should only be made when the comparisons are based upon identical indicators. Research leading to a uniform indicator definition and standard risk adjustment methodology is needed.