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Effect of a Diagnostic Imaging Pay-for-Performance Initiative on Imaging Costs: a Longitudinal Analysis

*Hui Cao, MS, Bio-Statistician 
Amanda Harrier, MPH, Health Care Manager 
Michael Paustian, PhD, MS, Health Care Manager 

Keywords: Pay-for-Performance; Diagnostic imaging; Generalized linear mixed models; Longitudinal analysis

Our purpose was to determine the effect on imaging costs of a diagnostic imaging pay-for-performance initiative available to physician organizations (POs) in the Physician Group Incentive Program beginning in 2008. We collected annual initiative participation status and monthly diagnostic imaging costs for 99 POs from January 2006 to December 2010. Member characteristics (including age, gender, and an episode-based risk assessment) and per member per month (PMPM) costs were aggregated by PO for primary care attributed commercial members. We applied generalized linear mixed models with a 6-month program ramp-up to estimate the mean effect of initiative participation on imaging costs, adjusting for PO and member characteristics. The mean diagnostic imaging PMPM cost at initiative onset was $27.16, increasing monthly by $0.11 PMPM. During the 6-month ramp-up, the mean diagnostic imaging PMPM for initiative participants decreased by $0.80 PMPM (3%), and the monthly trend fell to $0.04 PMPM. After ramp-up, the monthly trend fell to $0.02 PMPM. By December 2010, the mean diagnostic imaging PMPM for initiative participants was $3.54 (9%) lower than the predicted PMPM had they not participated. Decreases in overall diagnostic imaging costs and the monthly rate of increase were observed following initiative implementation, suggesting positive program impacts.