Measuring Self-Report Obsessionality in Anorexia Nervosa: Maudsley Obsessive–Compulsive Inventory (MOCI) or Obsessive–Compulsive Inventory-Revised (OCI-R)? Marion Roberts 1 , Anna Lavender 2 & Kate Tchanturia 1 * 1 Institute of Psychiatry, Department of Psychological Medicine, King’s College London, UK 2 Institute of Psychiatry, Department of Psychology, King’s College London, UK Abstract Self-report measures are often used in research and clinical practise as they efficiently gather a large amount of information. With growing numbers of self-report measures available to target single constructs, it is important to revisit one’s choice of instrument to be sure that the most valid and reliable measure is employed. The Maudsley Obsessive–Compulsive Inventory (MOCI) and the Obsessive–Compulsive Inventory-Revised (OCI-R) were admi- nistered to 223 female participants: 30 inpatients with anorexia nervosa (AN), 62 community cases with AN, 69 community cases weight restored from AN and 62 healthy controls. Both measures distinguished between clinical and healthy groups; however, the OCI-R showed superior internal reliability. Additionally, the OCI-R measures six (to the MOCI’s four) obsessive–compulsive constructs, and uses a more sensitive response format (likert scale vs. categorical). It is recommended that the OCI-R be employed as the self-report instrument of choice for assessing obsessive–compulsive pathology in those with AN. Copyright # 2010 John Wiley & Sons, Ltd and Eating Disorders Association. Keywords anorexia nervosa; obsessive–compulsive disorder; MOCI; OCI-R; psychometrics *Correspondence Dr Kate Tchanturia, PhD, Eating Disorders Unit PO59, Institute of Psychiatry, King’s College London, De Crespigny Park, London SE5 8AF, UK. Tel: 0044 207 848 0134. Fax: 0044 207 848 0181. Email: kate.tchanturia@iop.kcl.ac.uk Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/erv.1072 Introduction The high level of comorbidity and symptomalogical overlap between anorexia nervosa (AN) and obsessive– compulsive disorder (OCD) has long been acknowl- edged. Co-morbidity estimates of the proportion of AN sufferers with co-morbid OCD vary widely, from 17.5% (Godart et al., 2003) to 66% (Fornari, Kaplan, Sandberg, Matthews, Skolnick, & Katz, 1992). This considerable variation may in part be due to the wide range of measurement instruments employed to measure comorbid OCD in the AN literature. Clinically, high obsessive–compulsive symptomatology has been associated with poor treatment outcome (Rastam, Gillberg, & Wentz, 2003; Thomsen, 1994) and increased severity of eating disorder psychopathology (Jimenez-Murcia et al., 2007). The complexity of this picture underlines the need to be able to assess obsessive–compulsive symptoms in eating disorder patients quickly and easily in routine clinical practice (e.g. Davies, Liao, Campbell, & Tchanturia, 2009). In brief, reliable measurement Eur. Eat. Disorders Rev. (2010) ß 2010 John Wiley & Sons, Ltd and Eating Disorders Association.