02007nas a2200133   4500000000100000008004100001100001300042700001900055700001800074700002000092245015500112520159200267022001401859       2017                            d1 aLi Qiang1 aO'Connell Neil1 aKamper Steven1 aStevens Matthew00aTwin peaks? No evidence of bimodal distribution of outcomes in clinical trials of non-surgical interventions for spinal pain: An exploratory analysis.3 a<p>
<b>OBJECTIVE: </b>The presence of bimodal outcome distributions has been used as a justification for conducting responder analyses, in addition to, or in place of analyses of mean difference, in clinical trials and systematic reviews of interventions for pain. The aim of this study was to investigate the distribution of participants' pain outcomes for evidence of bimodal distribution.
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<b>STUDY DESIGN AND SETTING: </b>We sourced data on participant outcomes from a convenience sample of 10 trials of non-surgical interventions (exercise, manual therapy, medication) for spinal pain. We assessed normality using the Shapiro-Wilk test. Where the Shapiro-Wilk test suggested non-normality we inspected distribution plots visually and attempted to classify them. To test whether responder analyses detected a meaningful number of additional patients experiencing substantial improvements we also calculated the risk difference and number needed to treat to benefit (NNTB).
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<b>RESULTS: </b>We found no compelling evidence suggesting that outcomes were bimodally distributed for any of the intervention groups. Responder analysis would not meaningfully alter our interpretation of these data when compared to the mean between group difference.
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<b>CONCLUSION: </b>Our findings suggest that bimodal distribution of outcomes should not be assumed in interventions for spinal pain and do not support the automatic prioritisation of responder analysis over the between group difference in the evaluation of treatment effectiveness for pain.
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