What is new?
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Patients with chronic low back pain (LBP) need to see larger effects with nonsteroidal anti-inflammatory drugs (NSAIDs) than with physiotherapy to consider the intervention worthwhile.
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These estimates do not change over time and are in general not associated with symptom severity, duration, or mood.
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The smallest worthwhile effects elicited in this study reflect patients' opinions; are based on between-treatment differences; and consider the costs, risks, and inconvenience of intervention.
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We advocate the use of these estimates in sample size calculations and interpretation of trial findings of NSAIDs or physiotherapy for chronic LBP.
In 1989, Jaeschke et al. [1] defined the “minimum clinically important difference” as “the smallest difference in score in the domain of interest, which patients perceive as beneficial and which would mandate, in the absence of troublesome side effects and excessive cost, a change in the patient's management.” Since Jaeschke's seminal article, many studies have been conducted to ascertain the smallest worthwhile effects of a range of interventions. Robust estimates of the smallest worthwhile effect of interventions can be used to inform sample size calculations in clinical trials and to interpret the findings of clinical trials [2].
A recent systematic review located 31 studies and 129 estimates of the smallest worthwhile effect of interventions for nonspecific low back pain (LBP) [2]. Most of the studies identified in the review used anchor- or distribution-based methods. These methods have important limitations that, we argue, mean they should not be used to inform sample size calculation for clinical trials or to interpret treatment effects observed in clinical trials [2]. For instance, the review found that, of the 129 estimates elicited, only 5% were based directly on patients' judgments, only 4% were intervention specific (i.e., considered the costs, risks, and inconveniences of intervention), and all were based on changes in symptoms over time rather than on differences in outcomes with and without intervention. The latter is an important limitation of existing estimates because changes in outcomes that are measured over time may partly reflect not only the effects of intervention but can also be influenced by many other factors [3]. Effects of intervention can only be understood in terms of differences in outcomes with and without intervention [4], [5]. Thus, any attempts to identify the smallest worthwhile effects of intervention must define the smallest worthwhile effect in terms of the difference in outcomes with and without intervention [2].
In 2005, Barrett et al. [6], [7], [8] described the use of a form of contingent analysis, the “benefit–harm trade-off method,” to estimate the smallest worthwhile effect of health interventions. This method has been previously used to estimate the smallest worthwhile effect of interventions for the common cold [7], cancer therapies [9], [10], [11], [12], [13], [14], [15], [16], [17], and larval therapy [18]. It overcomes the limitations of anchor- and distribution-based methods because it captures the judgments of recipients of care; allows participants to weigh the benefits of treatment against the risks, costs, and inconveniences of treatment; and potentially provides estimates that are based on an intervention–control comparison.
In the present study, we use the benefit–harm trade-off method to elicit estimates of smallest worthwhile effect for two common treatments for nonspecific LBP, namely nonsteroidal anti-inflammatory drugs (NSAIDs) and physiotherapy (including manual therapy and exercise). In both cases, the comparator was no intervention. The aims of the study were to determine: (1) the distribution of the smallest worthwhile effect for NSAIDs and physiotherapy, (2) if patients assign different smallest worthwhile effects after 4 weeks of intervention, and (3) if duration or severity of symptoms (pain and disability) or mood (depression, stress or anxiety) is associated with these estimates.