Comparison between tools for measuring breathlessness: Cross-sectional validation of the Japanese version of the Dyspnoea-12

Introduction: The Dyspnoea-12 (D-12) is a brief, easy to complete questionnaire for measuring breathlessness. Objectives: To facilitate further efforts to measure dyspnoea in real clinical settings, the authors aimed to develop and validate a Japanese version of the D-12 and also compare the D-12 with the Baseline Dyspnea Index (BDI) and the Activity component of the St. George's Respiratory Questionnaire (SGRQ). Methods: The standardized procedure in accordance with international guidelines was used to create the translation. A validation study with a cross-sectional observational design was conducted on 122 subjects with stable chronic obstructive pulmonary disease (COPD). Results: The internal consistency of the D-12 was high (Cronbach's coefficient α = 0.883) and similar to that of the BDI (α = 0.824) and SGRQ Activity (α = 0.872). The relationships between tools were statistically significant (|R_s| = 0.53 to 0.66). Although the scores obtained from all three tools were skewed toward the milder end of the respective scales, this deviation was most prominent in the D-12 with a floor effect of 48.4%. Conclusion: The Japanese version of the D-12 was successfully validated, but we should be careful of any floor effect and marked skew to the mild end of the scale, especially in subjects with mild COPD.