OBJECTIVES:

Duchenne muscular dystrophy (DMD) is a rare, fatal, X-linked recessive disease that causes progressive muscular degeneration. The DMD-Specific Measures of Physical Functioning – Caregiver Questionnaire (DMD-CQ) is an observer-reported outcome developed to assess changes in physical function in ambulatory patients with DMD. The objective of this cognitive debriefing study was to evaluate the content validity of the DMD-CQ.

METHODS:

The DMD-CQ was cognitively debriefed in ten in-person interviews with caregivers of ambulatory patients with DMD, recruited through a patient advocacy group. The think-aloud method was used, which includes having caregivers state their thoughts while reading the questionnaire aloud. After the think-aloud exercise, the interviewer probed for additional feedback on areas that seemed confusing, and asked questions from an interview guide to elicit feedback on the instructions, recall period, items, and response choices. The interviews were audio-recorded, transcribed, coded, and analyzed.

RESULTS:

Caregivers came from a range of educational backgrounds, clinical trial experience, and demographics. Caregivers’ children with DMD represented a range of ages and disease severity. Caregivers found the DMD-CQ content to be appropriate and important for understanding disease progression in patients with DMD. The instructions were easy to understand, as were most of the items and their corresponding response choices. Caregivers found the response choices well-suited to their corresponding items. Seven of ten caregivers recommended making the recall period one month instead of one week. Feedback from the interviews also informed revisions to several items and responses to improve clarity.

CONCLUSIONS:

Interviews with caregivers confirmed the relevance of concepts covered by the DMD-CQ, and the comprehensiveness and comprehensibility of most of the items and their response choices. Feedback from caregivers was used to refine the recall period and improve several items and response choices for clarity. Future work includes psychometric validation.