“…In many of the research papers, the authors did not discuss the degree of attrition or the impact that such 'self-selection' bias may have had on the results. Eleven studies mentioned this issue as a consideration or limitation (Doherty et al, 2006;Duncan and Bardacke, 2010;Fabian et al, 2005;Fagan, 2008;Goto et al, 2010;Hartung and Hahlweg, 2010;Heinrichs and Jensen-Doss, 2010;Hiscock et al, 2008;Niccols, 2008;Patrick et al, 2008;Svensson et al, 2009). The combination of participant attrition and reach issues indicate that many programmes may be failing to engage parents and meet the goals of universality.…”