Exploring Episode-Based Approaches for Medicare Performance Measurement, Accountability and Payment Final Report. Attribution of Care to Providers


There is a wide array of attribution rules that can be used to assign episodes to providers of care. The rules can vary in terms of whether a single provider is assigned responsibility versus multiple providers being assigned responsibility. The particular types of services and the threshold used to allocate responsibility can also vary. The rules we used included some that used Evaluation and Management (E&M) visits to allocate responsibility, while others have used costs based on a broader set of professional services. Using E&M visits as the basis for accountability is frequently used in the context of performance measurement, whereby one is interested in determining which physician had the most responsibility for the "management" or trajectory of care.  Using attribution methods that include other Part B services or facility care may include services that have such high fixed costs, that they do not necessarily represent any relative level of management, but rather reflect the built-in costs of those services.  On the other hand, not including those types of services assumes little to no responsibility for managing the costs of those services or episodes for those that provide the procedures or the facility care.  

While there is no universally agreed upon definition of what constitutes "professional services," in previous work spent significant effort creating operational definitions for professional costs a based on a reduced set of HCPCS codes using E&M visits under CMS' Berenson Eggers Type of Service (BETOS) code definition as a starting point as described in Appendix F.

Previous work in attribution has looked at assigning care only to physicians. However, for the purposes of linking performance measurement or financial incentives to episodes, as noted previously, it may also be important to have attribution rules that assign care to facilities. Therefore, in addition to examining the performance of physician-based attribution rules that have been used by others, we introduced new rules that allow assignment of episodes to facilities. Table 16 presents a summary of the attribution rules used in these analyses. For example the "episode payments plurality" rule assigned an episode to the single MD that had the highest portion of professional services payments as long as they met the threshold of having at least 30 percent of the professional payments. If no MD met this threshold, attribution for the episode was not assigned under this rule.

The facility rule could be combined with physician/practice attribution rules to create shared facility-physician attribution rules - the next to the last row in Table 15 is an example of this. The last row of Table 16 includes a shared attribution rule that combines facility attribution with the attending physician for the hospital assigned responsibility for the episode. More sophisticated and complicated attribution rules could be created that utilize a hierarchy of attribution based on a series of if-then statements. For example, attribution could be an individual physician if they account for the majority of outpatient E&M visits; then if no physician met this criterion, attribution could be made to a facility.

Title of Rule Signal for Responsibility Single or Multiple Providers Relevant cut-off

Table 16: Design Characteristics of Episode-Based Attribution Rules

Episode Payments Plurality Professional Payments Single MD At least 30% professional payments
Episode Payments Multiple Physicians Professional Payments Multiple MDs All MD with >25%
Episode Visits Plurality E&M Visits Single MD At least 30% E&M visits
Facility Payments Plurality Facility Payments Single Facility At least 30% facility payments
Facility Payments Multiple Facilities Facility Payments Multiple Facilities At least 25% facility payments
Episode Payments Plurality + Facility Payments Plurality Professional Payments + Facility Payments Single MD + Single Facility Facility with at least 30% facility payments or MD with at least 30% professional payments

In Table 17 we present the portion of episodes related to three conditions, AMI, diabetes, and hip fracture, that could be assigned under each of the attribution rules. The majority of episodes could be assigned to a physician under all of the physician-based rules. While basing attribution on professional services payments resulted in only a small increase compared to the use of E&M visits in the number of episodes that could be attributed for diabetes (an additional 2.9 percent of episodes), the difference was more substantial for both AMI (and additional 12.8 percent of episodes) and hip fracture (an additional 14.2 percent of episodes). Similarly, while moving the threshold from 30 percent to 25 percent of professional services payments resulted in being able to attribute an additional seven percent of AMI-related episodes to physicians, this had much less of an impact on the attribution of diabetes-related episodes (increase of 0.6 percent of episodes attributed) and hip fracture-related episodes (an additional 1.4 percent of episodes attributed).

The fraction of episodes that could be assigned to a facility varied greatly by condition. The variation is driven by whether facilities are involved in the care for episodes related to that condition. For example, 99.2 percent of episodes related to AMI include inpatient care and 93.0 percent of all episodes related to AMI can be assigned to a facility. In contrast, 14.8 percent of episodes related to diabetes involve inpatient care and only 8.4 percent of episodes can be assigned to a facility.

Attribution Rule AMI Diabetes Hip Fracture

Table 17. Percent of Episodes Assigned Using Various Attribution Rules, ETGs

Episode Visits Plurality 73.4% 82.2% 81.7%
Episode Payments Plurality 86.2% 85.1% 95.9%
Episode Payments Multiple Physician 93.2% 85.7% 97.3%
Facility Payments Plurality 93.0% 8.4% 89.7%
Facility Payments Multiple Facilities 93.0% 8.4% 89.8%
Episode MD Payments Plurality or Facility Payments Plurality 98.9% 86.3% 98.6%

There may be concerns that if beneficiaries receive care in many settings, their care could be fragmented and it might be difficult to identify a provider who meets the minimum thresholds for attributing episodes. The data supported this concern for some, but not all, of the conditions. In general, the more settings that were involved in an episode, the more likely an episode could be assigned to a facility (i.e., the episode was more likely to involve inpatient care). Also, when multiple settings were involved, the facility care was typically the most costly.  Despite representing a large portion of the total costs, it is unclear whether the facility should have much responsibility over overall costs or quality of the episode, given that the decision to admit a patient to a facility may have occurred outside of the facility (i.e., with the ambulatory physician). For physician-based rules, the results were mixed.

Figure 22. Relationship between Number of Settings Involved in Episode and Attribution

Relationship between Number of Settings Involved in Episode and Attribution

Figure 22 shows the relationship between the number of settings involved in an episode and the percent of ETG episodes that could be assigned based on the episode professional services payment plurality rule (single provider accounting for at least 30 percent of professional services payments) for AMI, diabetes and hip fracture. While the percent of episodes related to AMI that were able to be attributed to a physician initially increased with the number of settings, there was a substantial drop-off when the episode involved four or more settings. This drop-off was very small, however for diabetes and hip fracture.

The previous table and figure show that episodes can be assigned to providers, but this does not guarantee that the attribution will have face validity with the provider. While a majority of the costs of care in an episode with a facility admission will be driven by the facility costs, it may be less clear whether the physician who delivered care before the admission or the physician who managed the patient inside the admission had more responsibility over the costs of that episode and how to divide responsibility. Of potential concern is that an assigned provider, either a physician or a facility, may actually provide a relatively small fraction of the care in terms of costs and that this may create face validity problems in making the assignment.  

This is borne out in the data. In Table 18 we show results for three rules: "episode payments plurality", "facility payments plurality" and "episode payments plurality + facility payments plurality." We show data for ETG episodes; MEGs produce similar results. The fraction of payments for services delivered by the provider(s) to which the episode is attributed varies substantially by both attribution rule and condition; a rule with a high fraction for one condition may have a low fraction for another condition. Rules that assign care to both a physician and a facility had a larger fraction of payments being delivered by the responsible provider. These data show the utility of multiple attribution, but also raise questions regarding if the rule were based on single attribution to a physician and multiple physicians are involved, which physician is more responsible for managing the costs of the episode? The preferred attribution rule would likely be determined by what is trying to be accomplished from a policy perspective, the type of episode that is being measured, and the application.

Table 18. Percent of Payments from Services Provided by Attributed Providers

Attribution Rule

Condition Episode Payments Plurality Facility Payments Plurality Episode Payments Plurality + Facility Payments Plurality
AMI -  6.5% 66.4% 73.0%
Diabetes 29.0% -  5.0% 34.0%
Hip Fracture -  8.9% 54.3% 63.1%

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