What are the advantages and disadvantages of doing this type of research?

Read and review the article “The ambient ozone and COVID-19 transmissibility in China: A data-driven ecological study of 154 cities.” You can get a copy here:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7342057/
This is an ecological study. Answer:
1. What is the level of analysis? Comment on the strengths and weaknesses of the study.2. Would this be enough evidence to change clinical practice or public policy? Why or Why not?3. Where does this study fall in the hierarchy of evidence?4. What are the advantages and disadvantages of doing this type of research?
The post should be 250 words or less.