ObjectiveTo determine whether and to what degree bias and underestimated variability undermine the predictive value of preclinical research for clinical translation.
MethodsWe investigated experimental spinal cord injury (SCI) studies for outcome heterogeneity and the impact of bias. Data from 549 preclinical SCI studies including 9,535 animals were analyzed with meta-regression to assess the effect of various study characteristics and the quality of neurologic recovery.
ResultsOverall, the included interventions reported a neurobehavioral outcome improvement of 26.3% (95% confidence interval 24.3-28.4). Response to treatment was dependent on experimental modeling paradigms (neurobehavioral score, site of injury, and animal species). Applying multiple outcome measures was consistently associated with smaller effect sizes compared with studies applying only 1 outcome measure. More than half of the studies (51.2%) did not report blinded assessment, constituting a likely source of evaluation bias, with an overstated effect size of 7.2%. Assessment of publication bias, which extrapolates to identify likely missing data, suggested that between 2% and 41% of experiments remain unpublished. Inclusion of these theoretical missing studies suggested an overestimation of efficacy, reducing the effect sizes by between 0.9% and 14.3%.
ConclusionsWe provide empirical evidence of prevalent bias in the design and reporting of experimental SCI studies, resulting in overestimation of the effectiveness. Bias compromises the internal validity and jeopardizes the successful translation of SCI therapies from the bench to bedside. Glossary BBB = Basso, Beattie, Bresnahan; BMS = Basso Mouse Scale for Locomotion; CAMARADES = Collaborative Approach to Meta-Analysis and Review of Animal Data From Experimental Studies; CI = confidence interval; OEG = olfactory ensheathing glia; SCI = spinal cord injury.To allow a more homogeneous group characterized by similar effect sizes (ESs), a rodent analysis was completed identifying the Basso, Beattie, and Bresnahan (BBB)/Basso Mouse Scale (BMS) only group as comparable with regard to the main outcome parameter (improved locomotor function, figure 1B, red square). Funnel plots illustrating the precision (1 divided by the SEM, y-axis) plotted against the standardized ES (x-axis). Each black dot represents 1 experiment. In the absence of publication bias, the points should resemble an inverted funnel. Black dotted line indicates the reported ES before inclusion of missing studies; red line, after trim and till analysis. (A) Decompression: reported ES 27.1% (95% confidence interval [CI] 15.1-39.1, n = 22 studies), adjusted ESs 12.8% (95% CI 1.7-24.0, n = 31). (B) Exercise: reported ES 14.4% (95% CI 6.4-22.3, n = 35), adjusted ES 1.9% (95% CI −6.9 to 10.7, n = 42). (C) Hypothermia: reported ES 16.3% (95% CI 10.3-22.3) without adjustments. (D) Olfactory ensheathing glia (OEG): reported ES 20.1% (95% CI 15.2-24.9, n = 53), adjusted ES 19.2 (95% CI 14.4-24.0, n = 54). (E) Rho/ROCK inhibitors: reported ES 21...