The political polarization of health outcomes in the USA

Summary

Health dataTo explore the relationship between politics and health, we draw on the Add Health survey. Add Health is an ongoing survey tracking a nationally representative cohort in the USA, first interviewed while in grades 7–12 in 1994. So far, this cohort has been interviewed five times.Add Health interviews include survey questions on demographic and health attributes and measurements of ‘biomarkers’ collected in survey takers’ homes by trained interviewers. Five biomarkers are measured in both waves 4 and 5, which are our focus here: body mass index, lipids (that is, cholesterol), HbA1c levels, blood pressure and C-reactive protein levels. Add Health has also checked respondents’ vital status against the National Death Index up to 2022 to determine whether respondents have died. Because of their age, mortality is a rare, although important, outcome in this sample: those interviewed in wave 5 were born between 1974 and 1983, with over 92% born between 1977 and 1982. By 2021–2022, the cohort was largely between 40 and 45 years old.In the third (2001–2002), fourth (2008–2009) and fifth (2016–2018) survey waves, Add Health also asked respondents whether they identified as very liberal, liberal, moderate, conservative or very conservative. Although Add Health does not have a usable measure of party identification or vote choice, it is worth emphasizing that its inclusion of any questions about political orientation makes it unusual among health surveys.Due to Add Health’s school-based sampling design, standard errors are clustered at the school level. All data are weighted to be representative of the cohort in the given wave.Ideology and health markers during the lifetimeFigure 1 shows the average number of comorbidities (out of five measured biomarkers; see Methods for details) for liberals and conservatives, as measured in waves 4 and 5. Higher numbers represent more total comorbidities and thus poorer health (Supplementary Section 1 presents results by individual ...