Estimating the Effect of Physical Education Reform on College Students' Mental Health with Difference-in-Differences

Facing increasingly fierce competition, mental health issues among college students have become a growing concern in higher education. College physical education (PE) plays a vital role in improving mental health among students. However, its causal effects and potential mechanisms remain insufficiently studied. In this study, we use a difference-in-differences (DID) model to investigate the impact of PE reform on college students' mental health. To address individual heterogeneity, common time trends, and potential sample selection bias, the propensity-score matching DID (PSM-DID) method was applied. We analyzed 3066 student-wave observations from 1533 unique students at universities in 26 Chinese cities during 2021-2024; each student was observed in two survey waves. The intervention was a one-year compulsory PE reform involving adjustments to course design and expanded opportunities for physical activity. Students attending reform-adopting universities in 15 cities constituted the treatment group, while students attending universities without the reform in 11 cities formed the comparison group. A time-varying difference-in-differences model, supplemented by propensity-score matching, examined changes in CES-D-10 depressive-symptom scores using city-level reform adoption dates. Results show college PE reform significantly reduced CES-D scores. In the fully adjusted university- and wave-fixed-effects model with city-clustered standard errors (26 cities), PE reform was associated with a 1.22-point reduction in CES-D scores (β = -1.22; SE = 0.38; 95% CI: -1.96 to -0.49; wild cluster bootstrap p = 0.019). Excluding self-rated mental health left the estimate essentially unchanged (β = -1.24). On the matched sample, with SH omitted from the propensity-score model, the corresponding estimate was β = -1.28 (N = 1974). A formal interaction test indicated a larger effect in first-tier cities (p = 0.014); academic-year differences were jointly significant (p = 0.043). Mechanism analysis further indicates that PE reform was also associated with increased exercise habit intensity and exercise frequency, suggesting potential behavioral channels. This study shows benefits of college physical education reform for mental health and offers important policy implications.