Bradford Hill criteria

https://www.ncbi.nlm.nih.gov/m/pubmed/26646432/

https://www.tandfonline.com/doi/abs/10.1080/10408398.2010.526838

https://pdfs.semanticscholar.org/2db8/b45ec77d62319c6bf7aa04bc8498345ab889.pdf


https://jamanetwork.com/journals/jama/fullarticle/2698337?utm_source=facebook&utm_campaign=content-shareicons&utm_content=article_engagement&utm_medium=social&utm_term=082418#.W4AhfpCy4tI.facebook