Identifying the causal effects of long-term exposure to PM2.5 and ground surface ozone on individual medical costs in China—evidence from a representative longitudinal nationwide cohort

Table 3 Estimation results of the effects of ground surface ozone on the total medical costs

Variables	ln (total medical fees)		Total medical fees
	(1)	(2)	(3)	(4)	(5)
	Linear regression	Fixed-effects 2SLS	Pool-Tobit	Tobit-CRE	Tobit-CRE-CF
Ground surface ozone	− 0.009***	0.023	− 4.859	46.420**	198.626*
	(0.001)	(0.019)	(6.752)	(16.254)	(87.428)
Ozone_residual	-	-	-	-	− 156.447
	-	-	-	-	(91.514)
Other control variables	Yes	Yes	Yes	Yes	Yes
Year dummy	Yes	Yes	Yes	Yes	Yes
Correlated random effects	No	No	No	Yes	Yes
N	26,784	26,784	26,784	26,784	26,784
R²	0.341	0.192	-	-	-
Cragg-Donald Wald F statistic		241.401 > 19.93	-	-	-
Sargan statistic		0.898(P = 0.343 > 0.05)	-	-	-

Note: (1) Standard errors in parentheses; (2) Other control variables include a set of covariates; (3) Correlated random effects: a linear combination of endogenous variables, instrumental variables and covariates; (4) *p < 0.05, **p < 0.01, ***p < 0.001

ISSN: 1741-7015