Construct validity and temporal stability of the abridged 31-item Illness Behaviour Questionnaire

Objective: Key psychometric information was sought for three newly derived dimensions from an abridged Illness Behaviour Questionnaire (IBQ-31): Affirmation of Illness (AI), Concern for Health (CH) and General Affective State (GAS). The construct validity of these scales was examined along with their test-retest reliability and long-term stability.Design: A longitudinal, observational study was conducted with 675 participants (general community members and those with either asthma, diabetes and chronic pain or chronic fatigue syndrome) providing self-report questionnaire data at baseline, with additional information sought at three (n = 483; 71.6%) and 12 months (n = 517, 76.6%).Main outcome measures: Construct validity of the IBQ-31 was explored using well-validated psychological measures of Symptom Attributions and Symptom Experience, Cognitive Distortion of Somatic Information and Illness Likelihood.Results: In general, AI, CH and GAS shared predictable empirical overlap with related psychological indices across the five samples. Adequate three-month test-retest reliability was evident, with greater score variability over 12 months.Conclusion: The IBQ-31 comprises three theoretically relevant dimensions which demonstrate relative short- and long-term stability for individuals with diverse illness experiences. Future investigations should explore the predictive validity of AI, CH and GAS, along with the potential value of 'cut-off' scores for clinical use.