Zip Codes May Not Be an Adequate Method to Risk Adjust for Socioeconomic Status Following Total Joint Arthroplasty at the Individual Surgeon Level

Abstract

BackgroundIncreasing consumerism in healthcare has included a push toward the ranking of individual surgeons. These rankings rely on the adjustment of patient outcomes based on individual patient risk. Socioeconomic status (SES) has been identified as an important variable impacting patient outcomes following total joint arthroplasty, and patient zip code has been proposed as a proxy. Our study attempts to determine if zip code is an acceptable proxy for SES within a single surgeon’s practice. MethodsUsing public zip code and Geographic Information Systems (GIS) tax map data, we compared the real estate holdings of 244 patients undergoing total joint arthroplasty from an individual hip and knee arthroplasty surgeon’s practice within an academic medical center over a 14-month period. An independent t-test was used to compare GIS data with the average home value within a given zip code. A Pearson correlation coefficient was calculated between GIS values and average home value per zip code. ResultsIn a sample of 244 patients, mean home value calculated from GIS data was $335,993 (standard deviation [SD] $246,549), and $243,663 with zip code data (SD $84,731). The Pearson correlation coefficient was 0.411 (P < .001). There was a significant difference between mean home values calculated from zip code data and GIS data (P < .001). Using zip code estimates would have mischaracterized home value, as defined as greater than or less than 1 SD, in 15% of patients. ConclusionAlthough there was some relationship between zip code and real estate holdings, the correlation is only moderate in strength and a substantial number of outliers were present. Given the sample size at the individual surgeon level, we question whether zip code can be used as a proxy for SES risk adjustment for the purposes of surgeon ranking.