The nature and assessment of mental contamination: A psychometric analysis

• The psychometric properties of three new scales to assess mental contamination were assessed.
• The three scales show excellent psychometric properties in both clinical and nonclinical samples.
• The new scales predict OCD symptoms over and above beliefs, depression/anxiety and a measure of traditional contact-based contamination fear.

There has been a recent expansion of interest in the concept of mental contamination. Despite a growing number of experiments and interview-based studies of mental contamination, there is a need for questionnaire-based assessment measures, and for a further understanding of the degree to which mental contamination is related to other aspects of OCD symptomatology and/or to established cognitive constructs relevant to OCD. We assessed the psychometric properties of three new measures of mental contamination (the Vancouver Obsessional Compulsive Inventory—Mental Contamination Scale, the Contamination Sensitivity Scale, and the Contamination Thought-Action Fusion Scale) in participants diagnosed with OCD (n=57), participants diagnosed with an anxiety disorder other than OCD (n=24) and in undergraduate student controls (n=410). For some of these analyses, our OCD sample was subdivided into those with contamination-related symptoms and concerns (n=30) and those whose OCD excluded concerns related to contamination fear (n=27). Results showed that the three new scales had excellent psychometric properties, including internal consistency, convergent and divergent validity, and discriminant validity. Further, the new measures accounted for significant unique variance in OCD symptoms over and above that accounted for by depression, anxiety, traditional contact-based contamination, and OCD beliefs. Results are discussed in terms of the clinical utility of the scales, and of the nature of contamination fears in OCD.