Summarized information of the studies included in meta-analysis.

aAccording to the universally agreed standard(population size, GDP, et al.), china cities is divided into three categories, including level A cities (large cities), level B cities (medium-sized cities) and level C cities (small cities). bgeographic areas refers to geographic location of china cities, including southern (S: southern) cities and northern (N: northern) cities. cGP: General population; PP: Permanent population. dNR: not reported in original paper; NA: not available.