Development and evaluation of a questionnaire instrument for chemical intolerance, based on the International Classification of Functioning, Disability and Health

Purpose: The purpose was to develop a questionnaire instrument to measure difficulties in activities and participation, and impact of environmental factors in chemical intolerance, based on the International Classification of Functioning, Disability and Health, and to assess its validity and reliability. Method: Development in three steps: (1) choosing items of relevance for chemical intolerance with an expert group, (2) conducting interviews with persons with chemical intolerance, using sampling to redundancy, (3) conducting a survey with 112 respondents at a first assessment and 91 at a second assessment for test-retest. Results: The final version of the instrument consists of 57 items divided in three parts, which showed good internal consistency in each part, Cronbach alpha: 0.73?0.87. It had good content validity, readability and face validity. Test-retest showed good to very good (?0.61) Kappa agreement for 37 items, and moderate (0.41?0.60) for 17 items. Three items had poor or fair (<0.41) Kappa agreement. Conclusion: The instrument was found to be valid and reliable. It can be used as a clinical tool to help persons with chemical intolerance to receive the best suited help and support for each individual, identify key points in rehabilitation, measure rehabilitation outcome and establish priority for treatment.