The smallest worthwhile effect of exercise therapy for people with chronic low back pain: a discrete choice experiment study

INTRODUCTION Understanding the magnitude of treatment effect patients need to see to consider a treatment worthwhile is of clear clinical and research importance. Current measures of clinical importance, such as the minimum clinical important difference, are limited as they are not determined by patients, and do not reflect specific costs, risks or inconveniences of individual treatments, i.e. you could have the same MCID for surgery as for exercise. We aimed to identify the smallest worthwhile effect (SWE), a new measure of clinical importance, of exercise therapy for people with non-specific chronic low back pain (CLBP) using discrete choice experiment. METHODS The SWE was estimated as the lowest reduction in pain that participants would consider exercising worthwhile, compared to not exercising i.e., effects due to natural history and other components (e.g., regression to the mean). We recruited English-speaking adults in Australia with non-specific CLBP to our online survey via email from a registry of previous participants and advertisements on social media. We used discrete choice experiment to estimate the SWE of exercise compared to no exercise for pain intensity. We analysed the discrete choice experiment using a mixed logit model, and mitigated hypothetical bias through certainty calibration, with sensitivity analyses performed with different certainty calibration thresholds. RESULTS 213 participants completed the survey. Mean age (±SD) was 50.7±16.5, median (IQR) pain duration 10 years (5-20), and mean pain intensity (±SD) was 5.8±2.3 on a 0-10 numerical rating scale. For people with CLBP the SWE of exercise was a between-group reduction in pain of 20%, compared to no exercise. This means, for a baseline pain of 5, the SWE would be a 1/10 between-group reduction in pain. CONCLUSION This patient-informed threshold of clinical importance should guide the interpretation of findings from randomised trials and meta-analyses of exercise therapy compared to no exercise.