Examines whether hospital size impacts the ability to identify hospitals' performance in a pay-for-performance demonstration project based on hospital rankings. Using data from the Premier Hospital Quality Incentive Demonstration and the Centers for Medicare and Medicaid Services' Hospital Compare, the report found that the smallest hospitals would, on average, experience five to seven times more uncertainty than the largest hospitals concerning their true relative performance for heart failure, pneumonia, and acute myocardial infarction. The authors conclude that all estimates of rank need to include adequate measures of uncertainty of those estimates.