Chance, Bias, and Confounding: Threats to Valid Measurement of Quality in the Context of Pediatric Cardiac Surgery

Assessment of quality in pediatric cardiac surgery has frequently been an add-on to efforts to measure adult cardiac surgery, without sufficient acknowledgement of the differences between the specialties. As a result, data reporting has often proceeded without adequate attention to data analysis. Assessment of clinical outcomes relies on the methods of observational epidemiology. Interpretation of the results of such investigations requires an understanding of the limitations inherent in the design of observational studies: chance, bias, and confounding. These limitations are of particular importance when studying pediatric cardiac surgery because of the relatively low number of cases performed at any one institution or by any one surgeon, the diversity of operations, and the heterogeneity of the congenital cardiac patient population.