A comparison of retrospective attribution rules.

OBJECTIVES

To compare the performance of methods to retrospectively attribute patients to provider systems by comparing the fraction attributed and the stability of assignment over time.

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

Descriptive statistics are used to measure the fraction of patients attributed and stability of attribution from year to year. This study uses a panel of administrative claims data (2010-2011). Attribution rules were defined by unit of measure (count of physician visits, dollars paid), type of providers (primary care physicians [PCPs], all physicians), type of encounters (all visits, evaluation and management visits only), and level of concentration of care (majority, plurality). We created 32 retrospective attribution rules, spanning PCP-only rules, all-physician rules, hierarchical rules based on PCPs then all physicians, and lookback rules based on current-year PCP visits then prior-year experience.

RESULTS

All methods exhibit a tradeoff between stability of attribution and fraction of the population attributed. This tradeoff is minimized when PCP-based rules are supplemented by a 1-year lookback when the current-year experience does not result in attribution.

CONCLUSIONS

We recommend using this lookback method when multiple years of data are available. In absence of multiple years of data, PCP-based rules maximize stability; hierarchical rules result in a greater fraction attributed with less loss of stability than simple all-provider rules.