Covariates
The covariates included characteristics at the individual and county level. Individual-level characteristics included age group (15-34, 35-59, ≥60 years old), gender (male, female), marital status (married, unmarried), educational level (primary school or below, junior middle school, senior middle school, college degree or above), annual household income, self-rated health (very poor, poor, fair, good, very good), diabetes mellitus (yes, no), hypertension (yes, no), and health insurance (yes, no). County-level characteristics included population size, county gross domestic product (GDP), and health human resources (ratio of physicians with bachelor’s degree or higher in the total number of licensed physicians). We selected these covariates to include relevant sociodemographic, health status and health system characteristics that may confound or mediate the relationship between PA and healthcare utilization.