Minimally Important Change and Smallest Detectable Change of the Oslo Sports Trauma Research Center Questionnaire in (Half) Marathon Runners
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Background: The Oslo Sports Trauma Research Center Questionnaire (OSTRC) severity score (sum of the four OSTRC question answer scores) measures the impact of a running-related injury (RRI). The smallest detectable change (SDC) and minimally important change (MIC) of the OSTRC severity score are currently unknown. Aim To evaluate the SDC and MIC of the OSTRC severity score in injured (half) marathon runners. Methods: Data from a prospective cohort study, the SUMMUM-2017 study, was used. A 133 runners who reported the same RRI on two OSTRCs two weeks apart, and filled in the global rating of limitations (GRL) and global rating of change (GRC) anchors were analyzed. Using the anchors, runners were classified as truly improved, unchanged, or truly worsened. SDC values were calculated at a group and individual level. MIC values were evaluated using the visual anchor-based MIC distribution and mean change method. Results: SDC values at a group level and at individual level were ≤0.27 and ≤5.91 respectively. The MIC was calculated using two methods. Visual anchor-based MIC distribution method: MIC for RRIs that truly improved on the GRC and GRL anchors were 13.50 and 18.50 respectively. Mean change method: MIC for RRIs that truly improved on the GRC and GRL anchors were 15.49 (95% CI 7.48-23.49) and 45.38 (95% CI 27.45-63.30) respectively. For RRIs that truly worsened a MIC value was only calculated using the mean change method with the GRL anchor 27.71 (95% CI -64.98-9.55). Conclusion: The OSTRC severity score MIC can distinguish between RRIs that truly improve and RRIs that were unchanged over a two-week period. The SDC was smaller than the smallest difference between any of the answer scores of the OSTRC questions. Furthermore, answers on the OSTRC questions need to improve by at least three options for the OSTRC severity change score to exceed the MIC value of 18.50. Implications of key findings: The MIC of 18.50 can be used in the process of monitoring a runner and help to determine if the RRI status truly improved or not. Furthermore, future studies could use the MIC values for sample size calculations.