Fig. 4: Results of placebo analysis on GFPZ policy.

(1) We conduct a series of placebo studies by iteratively applying the SCM used to estimate the effect of the GFPZ policy on every other province in the donor pool. Panels a–e represents Guangdong, Guizhou, Zhejiang, Jiangxi, and Xinjiang, respectively. The gray lines show the difference in value realization rate between each province in the donor pool and its respective synthetic version. The superimposed black line denotes the gap estimated for pilot provinces. (2) As the figure shows, the estimated gap for Guangdong, Guizhou, Xinjiang, and Zhejiang during the policy implementation period is unusually large relative to the distribution of the gaps for the provinces in the donor pool. The significance level of policy effect in Jiangxi is relatively weak. (2) There is still no denying the positive effect of the GFPZ policy on ecosystem product value realization.