Dyspnea Index: An upper airway obstruction instrument; translation and validation in Swedish.

OBJECTIVE Upper airway dyspnea is a challenging condition in which assessing the discomfort experienced by the patient is essential. There are three patient-reported outcome (PRO) instruments developed particularly for this patient group, none of which is available in Swedish. The aim of this study was to translate the Dyspnea Index (DI) into Swedish and validate the instrument for use in the Swedish-speaking population by investigating its basic psychometric properties. DESIGN A prospective instrument validation study. SETTING Tertiary referral center. PARTICIPANTS Fifty-three (n=53) patients with upper airway dyspnea and 19 healthy controls. MAIN OUTCOME MEASURES The questionnaire was translated into Swedish (swDI) with a forward-backward method. Reliability, repeatability, responsiveness and construct validity were assessed by asking the subjects to complete the swDI, a visual analog scale (VAS) at exertion and at rest and the Voice Handicap Index (VHI). RESULTS The swDI showed excellent internal consistency (Cronbach's α: 0.85) and repeatability (interclass correlation coefficient: 0.87 and Pearson's r: 0.89) in the patient group. No ceiling effect was observed (maximum score achieved was 39; 85% of the patients scored ≤36). SwDI scores moderately correlated with VAS at exertion (r: 0.59) and at rest (r: 0.42), yet poorly with the VHI (r: 0.36). The effect size (ES) was 3.8. CONCLUSIONS The swDI is a valid, robust and reliable questionnaire for self-assessment in Swedish-speaking patients with upper airway obstruction. A future anchor-based longitudinal study is needed to assess the smallest detectable change (SDC) and minimum important change (MIC) that were not estimated in our study.