Figure 1.

Flowchart of the sampling process. In stage two, two cities in each province other than Hubei were selected: the capital city with a relatively higher socio-economic level and higher level of the pandemic, and a non-capital city with a relatively lower socio-economic level and lower level of the pandemic. Four cities in Hubei were selected, the capital city and three non-capital cities, based on the same stratification method of social-economic level and the pandemic scale, because the Hubei was the most severely impacted by the pandemic.