“…We check the stationarity of the variables using nonstationary panel data methods [22][23][24][25][26][27]; in particular, according to [22,24], stationarity tests for series should be conducted before performing the panel regression; otherwise the regression may be spurious and this will result in misleading conclusions. And according to the Monte Carlo comparisons by [25,26], the second-generation panel unit root tests proposed by Bai and Ng [24] and Pesaran [28] are robust relatively, so we choose them in our empirical study. We found that both tests reject the null of unit root for the variables ℎ, , , V , , , , , 2 , 3 , , , and and are statistically significant at the 10% significance level, so we conclude that these variables are stationary.…”