Does the Union Make Us Strong? Labor-Union Membership, Self-Rated Health, and Mental Illness: A Parametric G-Formula Approach
Abstract Union members enjoy better wages, benefits, and power than non-members, which can improve health. However, the longitudinal union-health relationship remains uncertain, partially because of healthy-worker bias, which cannot be addressed without high-quality data and methods that account for exposure-confounder feedback and structural non-positivity. Applying one such method, the parametric g-formula, to United-States-based Panel Study of Income Dynamics (PSID) data, we analyzed the longitudinal relationships between union membership, poor/fair self-rated health (SRH), and moderate mental illness (Kessler-K6>5). The SRH analyses included 16,719 respondents followed from 1985-2017, while the mental-illness analyses included 5,813 respondents followed from 2001-2017. Using the parametric g-formula, we contrasted cumulative incidence of the outcomes under two scenarios, one in which we set all employed-person-years to union-member employed-person-years (union scenario), and one in which we set no employed-person-years to union-member employed-person-years (non-union scenario). We also examined whether the contrast varied by gender, gender-race, and gender-education. Overall, the union scenario did not reduce incidence of poor/fair SRH (RR: 1.01, 95% CI: 0.95, 1.09; RD: 0.01, 95% CI: -0.03, 0.04) or moderate mental illness (RR: 1.02, 95% CI: 0.92, 1.12; RD: 0.01, 95% CI: -0.04, 0.06) relative to the non-union scenario. These associations largely did not vary by subgroup.