Estimating Minimal Important Change of the National Institutes of Health Research Task Force impact score using computer adaptive measures: A secondary analysis of two randomized clinical trials in a military population with chronic pain

Abstract

Abstract Background The National Institutes of Health (NIH) Research Task Force (RTF) on Research Standards for Chronic Low Back Pain impact score is a composite measure of Patient Reported Outcomes Measurement Information System (PROMIS) pain intensity, pain interference and physical function. PROMIS surveys are available in short-form and computer adaptive testing (CAT) formats. In order to calculate response rates for clinical trials in which the impact score is the primary outcome, its minimal important difference (MID) must be established. To date, four estimates of impact score MID ranging from 3 to 7.5 have been published, and all were based on data collected using PROMIS short-form surveys. None used CAT versions of PROMIS surveys. Methods Secondary analysis of data collected during the conduct of two randomized clinical trials of 6-week courses of nonpharmacological pain therapies. Research subjects were US active-duty service members referred to an interdisciplinary pain management center. Impact score was assessed at the beginning and end of treatment. The Patient Global Impression of Change (PGIC) questionnaire was administered at the end of treatment and asked respondents to report their status compared to the start of treatment using a 7-item Likert scale ranging from very much improved to very much worse. A PGIC response of “much” or “very much” improved was used as the threshold for MID. Receiver operating characteristic curve (ROC) analysis was used to determine meaningful clinical differences for the full combined sample and stratified by study sample and baseline impact score. Results A decrease of 3 points was the estimated minimal important difference for the impact score. A larger decrease in impact score was needed for participants with moderate and severe baseline pain impact to report “much” or “very much” improvement. Conclusions Using data collected with CAT surveys, we calculated an overall MID of 3 for the NIH RTF impact score, and estimates ranged from 1 to 9 depending on the study sample and baseline impact score. These findings are consistent with previous MID estimates that were based on non-adaptive short form surveys and have implications for reducing the survey burden of future impact score MID analyses.