In Reply We agree with Maslove that there is no single rule to attribute patient outcomes to physicians.1 We used 3 different attribution rules: attributing patients to physicians who (1) accounted for the largest Part B spending, (2) derived the largest number of evaluation-and-management claims, and (3) derived the first evaluation-and-management claim. Our findings were similar in each approach. We also found that 51%, 22%, and 11% of Part B spending was accounted for the first, second, and third highest-spending physicians, respectively,2 suggesting that a single physician drives the majority of care rather than multiple physicians delivering care equally.