Applying mixed methods to pretest the Pressure Ulcer Quality of Life (PU-QOL) instrument

Pretesting is key in the development of patient-reported outcome (PRO) instruments. We describe a mixed-methods approach based
on interviews and Rasch measurement methods in the pretesting of the Pressure Ulcer Quality of Life (PU-QOL) instrument.

We used cognitive interviews to pretest the PU-QOL in 35 patients with pressure ulcers with the view to identifying problematic
items, followed by Rasch analysis to examine response options, appropriateness of the item series and biases due to question
ordering (item fit). We then compared findings in an interactive and iterative process to identify potential strengths and
weaknesses of PU-QOL items, and guide decision-making about further revisions to items and design/layout.

Although cognitive interviews largely supported items, they highlighted problems with layout, response options and comprehension.
Findings from the Rasch analysis identified problems with response options through reversed thresholds.

The use of a mixed-methods approach in pretesting the PU-QOL instrument proved beneficial for identifying problems with scale
layout, response options and framing/wording of items. Rasch measurement methods are a useful addition to standard qualitative
pretesting for evaluating strengths and weaknesses of early stage PRO instruments.