Creating a common scale for the conversion of qDASH and PRWHE scores.

The Quick Disabilities of the Arm, Shoulder and Hand Questionnaire and Patient Rated Wrist and Hand Evaluation are two outcome measures used commonly in hand surgery. We evaluated the structural validity of these two outcome measures using item response theory and then developed a common scale that both outcome scores could be mapped to. Factor analysis found that both outcome measures assess the same two health constructs: 'Pain' and 'Motor Function'. We developed two separate common scales for both subscales. Frequency density plots and Bland-Altman analysis suggested that these can be used to compare the scores of one instrument to the other. We present a look-up table allowing readers to map sum-scores from these outcome measures onto the common scales.