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.