Karpati, AdamGalea, SandroAwerbuch, TamaraLevins, RichardObjectives. We examined variability in disease rates to gain understanding of the complex interactions between contextual socioeconomic factors and health. Methods. We compared mortality rates between New York and California counties in the lowest and highest quartiles of socioeconomic status (SES), assessed rate variability between counties for various outcomes, and examined correlations between outcomes’ sensitivity to SES and their variability. Results. Outcomes with mortality rates that differed most by county SES were among those whose variability across counties was high (e.g., AIDS, homicide, cirrhosis). Lower- SES counties manifested greater variability among outcome measures. Conclusions. Differences in health outcome variability reflect differences in SES impact on health. Health variability at the ecological level might reflect the impact of stressors on vulnerable populations.Health EquityHealthResearchsocioeconomic factorsvariability in disease ratesmortality ratessocioeconomic statusHealth variabilityvulnerable populationsArticle