Abstract
Background
Complex interventions, such as exercise for LBP, often have many treatment targets. Matching a primary outcome to the target(s) of exercise interventions may provide greater standardized mean differences (SMDs) than using an unmatched primary outcome. We aimed to explore whether the conclusions of exercise trials for LBP might differ with i) improved matching of outcomes to treatment targets and ii) the use of composite outcome measures.
Methods and Results
We investigated i) matching in five trials (n=1033) that used an unmatched primary outcome but included some of their matched outcomes as secondary outcomes; ii) composite outcomes in four trials (n=864). The composite consisted of standardised averaged matched outcomes. All analyses replicated the primary outcome analysis, applied to the matched or composite outcome in each dataset. When not possible, SMDs were calculated for the primary and matched outcomes. i) Of five trials, three had greater SMDs and increased statistical significance with matched outcomes (pooled effect SMD 0.35 (95% CI 0.16, 0.54), p=0.0003) compared to an unmatched primary outcome (pooled effect SMD 0.13 (95% CI 0.04, 0.23) p=0.007). ii) Of four composite outcomes: two matched trials had greater SMDs and improved statistical precision in the primary outcome than the composite outcome; two unmatched trials had greater SMDs and improved statistical precision in the composite compared to the primary outcome.
Conclusion
Using an outcome that matches exercise targets in LBP trials appears to produce greater SMDs than an unmatched primary outcome. Future trials should consider primary outcome selection aligned with exercise treatment targets.
Sources of Funding: L Wood's PhD is funded by the Research Institute for Primary Care and Health Sciences, Keele University. Prof NE Foster is a UK National Institute for Health Research Senior Investigator, and was supported by a UK National Institute for Health Research Professorship (NIHR-RP-011-015). The views expressed in this publication are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health
Conflicts of interest: No conflicts of interest.
