Evaluating the Use of Zip Codes as a Proxy for Socioeconomic Status in Surgeon Ranking Systems: A Single-Center...

Introduction When comparing surgical outcomes for individual physicians, it is important to note the multifactorial element of socioeconomic status (SES) in recovery complications. Area-based measures of SES, like residential zip codes, are often used in risk-adjustment models. In this study, we sought to determine if residential zip codes are an accurate reflection of SES at the level of a single arthroplasty practice. Methods We conducted a retrospective study of 165 local residents who received a total knee arthroplasty (TKA) at our institution between May 2018 and May 2023. Primary residential addresses were collected from the electronic medical records. Individual property values were obtained from the local Central Appraisal District (CAD) website, and average zip code-level values were obtained directly from data provided by the CAD. Patients were excluded if their record address was a P.O. Box, apartment, or was missing from the electronic medical record. Results The mean individual home value was overestimated by an average of $32,497 (17.9%) by the mean zip code-based value (P = 0.0015). The Pearson correlation between the two variables (0.455) indicated a moderate association. Zip code estimates explained only 21% of the variance in the individual home values (R² = 0.21), and only 58.8% of patients had property values within one standard deviation of their zip code average. Conclusion Zip code-based SES adjustments explain only a small proportion of the heterogeneity evident in local, patient-level data and are prone to misclassification. For meaningful SES risk adjustment, particularly when evaluating surgeon performance or institutional rankings, precise, multifactorial approaches should be prioritized.