The Netherlands Obsessive Compulsive Disorder Association (NOCDA) study: design and rationale of a longitudinal naturalistic study of the course of OCD and clinical characteristics of the sample at baseline.

In half of Obsessive Compulsive Disorder (OCD) patients the disorder runs a chronic course despite treatment. The factors determining this unfavourable outcome remain unknown. The Netherlands Obsessive Compulsive Disorder Association (NOCDA) study is a multicentre naturalistic cohort study of the biological, psychological and social determinants of chronicity in a clinical sample. Recruitment of OCD patients took place in mental health organizations. Its design is a six-year longitudinal cohort study among a representative clinical sample of 419 OCD patients. All five measurements within this six-year period involved validated semi-structured interviews and self-report questionnaires which gathered information on the severity of OCD and its co-morbidity as well as information on general wellbeing, quality of life, daily activities, medical consumption and key psychological and social factors. The baseline measurements also include DNA and blood sampling and data on demographic and personality variables. The current paper presents the design and rationale of the study, as well as data on baseline sample characteristics. Demographic characteristics and co-morbidity ratings in the NOCDA sample closely resemble other OCD study samples. Lifetime co-morbid Axis I disorders are present in the majority of OCD patients, with high current and lifetime co-morbidity ratings for affective disorders (23.4% and 63.7%, respectively) and anxiety disorders other than OCD (36% current and 46.5% lifetime).