“…In several studies of attention and behaviour, those who primarily exhibit cleaning compulsions (washers) have been found to differ from those whose primary compulsions are not washing but checking or performing other rituals (termed non-washers or checkers; Ceschi, Van der Linden, Dunker, Perroud, & Brédart, 2003;Foa, Ilai, McCarthy, Shoyer, & Murdock, 1993;Matsunaga et al, 2002;S Moritz & von Mühlenen, 2008;Nedeljkovic et al, 2009;Omori et al, 2007;Phillips et al, 2000;Summerfeldt, Richter, Antony, & Swinson, 1999;Van der Linden, Ceschi, Zermatten, Dunker, & Perroud, 2005;. The heterogeneity of OCD can reduce the power of, and obscure, research findings unless sub-groups are considered (Hasler et al, 2007;Heyman, Mataix-Cols, & Fineberg, 2006).…”