Looking beyond administrative health care data:the role of socioeconomic status in predicting future high-cost patients with mental health and addiction

Introduction: Previous research has shown that the socioeconomic status (SES)-health gradient also extends to high-cost patients; however, little work has examined high-cost patients with mental illness and/or addiction. The objective of this study was to examine associations between individual-, household-, and area-level SES factors and future high-cost use among these patients. Methods: We linked survey data from adult participants (ages 18 and older) of three cycles of the Canadian Community Health Survey (CCHS) to administrative health care data from Ontario, Canada. Respondents with mental illness and/or addiction were identified based on prior mental health and addiction health care use and followed for 5 years for which we ascertained health care costs covered under the public health care system. We quantified associations between SES factors and becoming a high-cost patient (i.e, transitioning into the top 5%) using logistic regression models. For ordinal SES factors, such as income, education and marginalization variables, we measured absolute and relative inequalities using the slope and relative index of inequality. Results: Among our sample, lower personal income (OR=2.11, 95% C.I. [1.54, 2.88] for $0 to $14,999), lower household income (OR=2.11, 95% C.I. [1.49, 2.99] for lowest income quintile), food insecurity (OR=1.87, 95% C.I. [1.38, 2.55]) and non-homeownership (OR=1.34, 95% C.I. [1.08, 1.66]), at the individual and household levels, respectively, and higher residential instability (OR=1.72, 95% C.I. [1.23, 2.42] for most marginalized), at the area level, were associated with higher odds of becoming a high-cost patient within a 5-year period. Moreover, the inequality analysis suggests pro-high-SES gradients in high-cost transitions.