The Nijmegen Questionnaire: a valid measure for hyperventilation

Hyperventilation syndrome is often undiagnosed due to its multi-systemic and apparently unrelated symptoms. The Nijmegen Questionnaire is used by clinicians to assess susceptible individuals, based on self-reporting symptoms attributed to hyperventilation syndrome. However, evidence of psychometric properties of this questionnaire is lacking. This study investigated two types of validity, using interviews and Rasch analysis. Data showed that the Nijmegen Questionnaire met criteria for content validity but not for structural validity. Content validity was supported by a high matching percentage between the symptoms identified within interview data and the current items on the Nijmegen Questionnaire (94%). Reported symptoms from study participants were conceptually congruent with most of the questionnaire items with minor language inconsistencies between patients and clinicians. Rasch analysis indicated a poor fit of the Nijmegen Questionnaire to the Rasch model, demonstrating poor structural validity. This study also developed a revised version of the Nijmegen Questionnaire, which did meet criteria for structural validity. Subsequently, a conversion table was created for transforming raw total scores of the questionnaire in the clinical and research settings. Physiotherapists should use the revised 15-item Nijmegen Questionnaire for clinical and research purposes since it provides more accurate representation of the severity of patients’ symptoms than the original scoring.