Testing the psychometric properties of the illness perceptions questionnaire for OCD (IPQ-O)

Previous research has shown that our perceptions about illness are important determinants of how we respond and adjust to health threats. To examine whether illness perceptions affect illness responses in OCD (e.g. help-seeking), this study aimed to develop and test the psychometric properties of a new OCD-specific tool to assess illness perceptions, the illness perceptions questionnaire for OCD (IPQ-O).

A cross-sectional questionnaire-based design was used. Following adaptation of the IPQ-R based on qualitative interviews with people with OCD, adults (age ≥ 16) with OCD completed the IPQ-O (online or postal), alongside measures of depression, anxiety, OCD severity, attitudes to seeking mental health services and behaviours (e.g. treatment seeking intentions). A sub-sample re-completed the IPQ-O after two-weeks to obtain test-retest reliability. Factor analysis was used to derive the IPQ-O factor structure; internal consistency of subscales was calculated. Convergent validity was explored.

Three hundred forty-eight people with OCD completed the IPQ-O. After factor analysis, seven main sub-scales and four cause sub-scales were identified, explaining 45.5 and 41.6% of the variance after extraction and rotation respectively. Three sub-scales from the original IPQ-R were validated; other dimensions differed from original IPQ-R sub-scales. The new 'spectrum' sub-scale measures the strength of the view that OCD is a trait that presents to varying extents within the general population. The IPQ-O demonstrated internal consistency, test re-test reliability (Kendall's tau = .51-.75) and convergent validity. Illness perceptions were associated with important aspects of adjustment (depression, anxiety) and condition management (receipt of treatment, plans to seek help). In particular, emerging data showed that those who had not received medication for OCD endorsed stronger spectrum beliefs. Though longitudinal study is needed to verify the direction of this association, this raises the question of whether spectrum beliefs deter people with OCD from using pharmacological treatments.

The IPQ-O provides a valuable tool for subsequent testing of whether illness perceptions drive outcomes as proposed by the CSM. If perceptions are found to drive adjustment and behaviour, therapists could elicit and subsequently challenge perceptions that have negative effects on adjustment and coping, as part of psychological therapy.