Danish Version of 'The COPD Self-Efficacy Scale': Developing a 24-Item Version Using Rasch Analysis

The concept of self-efficacy has been utilised as a modifiable outcome supporting patients with chronic obstructive pulmonary disease (COPD). Self-efficacy refers to the individual's beliefs in their ability to manage or avoid breathing difficulties. For patients with COPD, some items in the original 34-item COPD self-efficacy scale (CSES) were not applicable or were irrelevant. The aim of this study was to develop a short version of the Danish version of CSES including a face validity test.

Rasch analysis was employed to assess the psychometric properties using a dataset from the validation study of the Danish version of CSES. Face validity test was used to identify possible challenges in the reduced version of the scale.

The analysis suggested two underlying factors, a physical (13 items) and an emotional (21 items). Evaluation on the reliability and accuracy estimates showed that the number of items within both factors could be reduced to 12, leaving a total of 24 items included in the CSES short version. The face validity test of the CSES short version showed that the length of the questionnaire was manageable, and the instructions were perceived clear and functional.

We found that the original COPD self-efficacy scale could be reduced from 34 to 24 items while still retaining acceptable levels of reliability and accuracy and with questions being comprehensible and relevant.