Essential public health service equalization and inequality of opportunity in health among internal migrants in China: a cross-sectional study using the 2017 China Migrants Dynamic Survey

China has promoted the equalization of essential public health services to improve migrants’ access to basic public health care. However, limited evidence exists on whether this policy is associated with reduced inequality of opportunity in health among internal migrants. This study examined the association between essential public health service equalization and health fairness gaps among internal migrants in China. Data were from the 2017 China Migrants Dynamic Survey. The analytic sample included 27,998 respondents, comprising 13,998 internal migrants and 14,000 local residents in pilot and non-pilot cities. Two health outcomes were examined: self-rated health and any common diseases in the past year. Health fairness gaps among internal migrants were estimated relative to local residents under ex ante and ex post compensation principles. Sampling weights were applied to migrant analyses. Propensity score matching was used to estimate the average treatment effect on the treated among internal migrants, with nearest-neighbour, stratification, and kernel matching applied as alternative matching methods. Confidence intervals for stratification and kernel estimates were obtained using 1,000 city-level fractional-weight bootstrap replications that repeated benchmark estimation, fairness gap construction, propensity score estimation and matching. For both outcomes, matched ex ante associations were not statistically significant under stratification or kernel matching. Pilot-city residence was associated with smaller ex post self-rated health fairness gaps across all three matching methods (ATT: -0.0472 to -0.0335). The stratification and kernel estimates were statistically significant (95%CIs: -0.0792 to -0.00004; -0.0777 to -0.0034, respectively). For the disease outcome, ex post estimates differed in direction across matching methods, and the stratification and kernel estimates were not statistically significant. Statistical significance for self-rated health and the direction of the disease estimates varied across benchmark specifications. Essential public health service equalization was associated with smaller ex post self-rated health fairness gaps among internal migrants, particularly after observed individual characteristics were considered. These findings extend the assessment of public health service equalization from service access to health equity relative to local resident benchmarks.