Eight studies were at risk of attrition bias because less than 80 of the sample was followed up Dor 2002; Franceschini 1994; Parazzini 1998; Rossing 2004; Shushan 1996; Stewart 2013; Trabert 2013; Van Leeuwen 2011; in five studies, this information was unclear Bjornholt 2015; Brinton 2013; Gronwald 2015; Kessous 2016; Rossing 1994 levitra allemagne