Development of the influence, motivation, and patient activation in diabetes (IMPACT-D™) measure

We sought to create a new research and clinical instrument –the Influence and Motivation for Patient ACTivation in Diabetes care (IMPACT-D™) - to measure the degree to which patients with type 2 diabetes (T2DM) value health and believe they can influence it. Candidate items were generated via a literature review, expert opinion, and qualitative interviews and focus groups with T2DM patients in Chicago, IL and Chapel Hill, NC. Psychometric testing guided by item response theory was conducted among an online panel of 500 English-speaking adults with T2DM. Differential item functioning analyses evaluated item performance across key participant characteristics. To determine construct validity, IMPACT-D™ scores were compared to other general measures of personality and patient activation. A second study among 300 patients recruited from two internal medicine clinics further assessed associations between the IMPACT-D™ and health outcomes. Cognitive interviews confirmed patient understanding of IMPACT-D™ items and instructions. Exploratory factor analyses revealed a single-factor solution that included 6 items. The IMPACT-D™ demonstrated adequate reliability (α = 0.72) and moderate construct validity with patient activation (r = 0.51, p