In creating profiles of the relative costs of care delivered by physicians, a number of methodological decisions must be made. We explored whether the choice of a rule for assigning costs to physicians affected the cost category to which physicians were assigned. We found that, compared to the most common rule used, 17% to 61% of physicians would be assigned a different category under an alternate attribution rule. Practically this means that if two health plans in a region chose different attribution rules, a physician will frequently be assigned a different cost category by the two health plans even if his or her care pattern was identical.(22
) Our findings are consistent with previous work that found that attribution rules applied to Medicare patients could affect the results of pay-for-performance programs.(8
) This result, however, diverges from what has been found in evaluating methods used to measure physician quality. In that literature, choice of attribution method has a relatively small effect on physicians’ quality profiles.(28
Our results help to explain why some physicians question cost profile attribution rules. No more than 60% of physicians’ billed costs were included in cost profiles under any rule. And of the physician costs assigned to a physician, up to two-thirds, were billed by other physicians. These findings might make physicians less responsive to efforts to use cost profiles to decrease spending. A related issue is what care assigned to a physician is truly “controllable” versus those costs that are driven by patient factors.(30
) To date, cut-offs such as 30% of the spending within an episode have been used as a method of determining assignment or control, but any such percentage cut-off is arbitrary and the appropriate cut-off may vary based on the condition being treated or the clinical scenario.
Given that the choice of attribution rule will lead to different conclusions being drawn about physicians’ cost performance, which rule is the best one? Unfortunately, there is no clear or simple answer to this question because “best” depends on what is important to each stakeholder and those perspectives vary. To illustrate this point we consider the views that might be held by a purchaser (health plan), a physician, and a patient. The purchaser is primarily interested in driving a change in the cost-related decisions of physicians, which will be easiest if the maximum number of physicians can be included in the profiling program. Using that criterion, the best rules include those that assign care to multiple physicians under which up to 66% of physicians having at least 30 episodes assigned.
From the physician perspective, the rule should accurately reflect what the physician is doing in practice. That means physicians might prefer profiles that capture a large proportion of their billed services and that reflect the care they billed rather than that billed by other providers. The best performing rule under the first criteria is the episode-based cost rule for multiple physicians which included on average 60% of a physician’s own costs in the profile. The best performing rule under the second criteria, that the profile does not include other physician’s care, is the episode-based, majority of costs, single physician rule in which 73% of the professional costs billed on average were by the physician being profiled.
From the patient perspective, the profiles should produce trustworthy information that is aligned with the decision the patient is being asked to make. Trust in the information will be undermined if the health plans in a region use different methods and different data because the different health plans will publicly report disparate results. Thus, patients are likely to be best served by efforts in which health plans pool their data and use consistent methods. Beyond that requirement, we might imagine two different types of choices being made by patients: choosing a primary care physician and choosing a specialist for consultation. In the case of choosing a primary care physician, the patient-based rules are most consistent with the decision being made. When a patient chooses a primary care physician they are in some sense choosing that physician and his or her referral network. Under a patient-based rule the physician assigned a patient’s costs is also assigned the costs provided by all the physicians caring for the patient. Alternatively, when choosing a specialist for a discrete reason, the episode-based rules are most consistent with the choice as the content of the profile is likely to be dominated by the types of services typically provided by those specialists.
There is no rule that best serves all perspectives. For this reason, transparency with respect to the methods used is critical. Purchasers will need to try and select a rule that balances these different perspectives. For example, in our study, under the episode-based cost multiple-physician rule, a high proportion of physicians were profiled and those profiles included a reasonably high proportion of physicians’ own costs.
Our analyses have several key limitations. We used aggregated data from four commercial health plans. Patients from a single health plan typically comprise a small fraction of a physician’s care. If we created cost profiles using a single health plan’s data, fewer physicians could be profiled. It is also unclear how our results generalize to Medicare beneficiaries who generally receive care from a larger number of providers than commercially insured patients, a difference which could make attribution more difficult.(8
) Although we tried to be comprehensive in our examination of attribution rules, there are variations in rules that we have not addressed. For example, some attribution rules use relative-value units rather than visits or costs as a signal for responsibility(22
) and cutpoints other than 30% and 50%.(12
) We also did not explore different attribution rules for different types of conditions.(31
) It could be argued that the disagreement rates between attribution rules we report are overestimates. As we describe in our supplementary appendix
, using statistical testing to categorize physicians results in lower, though still substantial, disagreement rates. Some health plans use two cost categories(22
) instead of the three used in our analysis, and using two cost categories will obviously result in lower disagreement rates. Also, in some cases a large fraction of the disagreement between attribution rules occurs because of the difference in the number of physicians with a low sample size (<30 episodes). The cut-off of 30 episodes was based on previous recommendations.(21
) If a higher or different threshold is used then our results would be different as fewer physicians would likely be included in any profiling effort.
The use of physician cost profiles has become more common. Our analyses emphasize that the choice of attribution rule affects how costs are assigned to physicians and that moving from one rule to another rule can make a difference in the cost category to which physicians are assigned. It is critical for health plans and others who create physician cost profiles to be transparent about how they assign costs to a physician. We hope these results prompt and inform a dialogue among stakeholders on which attribution rule should be used for different applications of cost profiles.