Methodological issues in the obsessive–compulsive spectrum

The obsessive–compulsive spectrum is a heterogeneous class of conditions. Recently, expert consensus has emerged regarding possible candidate disorders [Mataix-Cols, D., Petrusa, A., Leckman, J.F., 2007. Issues for DSM-V: How should obsessive–compulsive and related disorders should be classified. American Journal of Psychiatry, 164, 1313–1314]. Further, expert survey data suggest that obsessive-compulsive disorder is composed of overlapping subtypes. However, methodological approaches for testing whether candidate disorders properly belong in the spectrum have varied widely, and do not necessarily differentiate conditions from subtypes. We describe preliminary methodological and statistical recommendations for a systematic approach to determining what constitutes a subtype, how to determine inclusion in the spectrum, and means for ruling out candidate disorders.