In the paper they list two studies. Stellman et al. 1988 : http://www.sciencedirect.com/science/article/pii/0091743586900897 http://www.sciencedirect.com/scien

In the paper they list two studies. Stellman et al. 1988 : http://www.sciencedirect.com/science/article/pii/0091743586900897 http://www.sciencedirect.com/science/article/pii/00917435869... Fowler et al. 2008 : https://www.ncbi.nlm.nih.gov/pubmed/18535548 https://www.ncbi.nlm.nih.gov/pubmed/18535548