Determination of the minimal important difference for the acute otitis media severity of symptom scale

We previously developed and validated the acute otitis media severity of symptom (AOM-SOS) scale for rating symptoms of AOM in young children. In this report, we sought to estimate the minimal important difference (MID) for change in AOM-SOS scores. In a group of children 6-24 months of age with AOM enrolled in a recently reported placebo-controlled clinical trial of antibiotic efficacy, we compared changes in AOM-SOS scores with parental assessments of change over a 24-hour period. Mean absolute and mean relative change in scores in children reportedly exhibiting only a small degree of improvement were considered in arriving at an estimated MID. We then compared the proportions of children in the antibiotic and placebo groups, respectively, whose AOM-SOS scores changed more than the estimated MID at various time points after enrollment. Data were available for 277 children. Children whose parents reported only a small degree of improvement 24 hours after enrollment had a mean decrease in AOM-SOS score of 3.8, or 55%, from baseline. We found the relative decrease more telling than the absolute decrease. The proportions of children in the antibiotic and placebo groups, respectively, whose AOM-SOS scores had decreased