Important outcome predictors showed greater baseline heterogeneity than age in two systematic reviews

Does tranexamic acid prevent postpartum haemorrhage? A systematic review of randomised controlled trials

“…We then explored the success of the randomisation process by conducting meta‐analyses of selected baseline variables. As recommended by Clark et al . we meta‐analysed age as well as baseline haemoglobin (Hb), which we identified as another relevant prognostic covariate.…”

“…The premise of this analysis is that if the trials are properly randomised, there will be no heterogeneity, i.e. I 2 = 0% and any difference in baseline variables will be minimal and the result of random error . Figures S3 and S4 show the results of the meta‐analyses of age and baseline Hb.…”

Baseline imbalances and clinical outcomes of atypical antipsychotics in dementia: A meta‐epidemiological study of randomized trials

“…Third, we performed meta-analyses to calculate the pooled mean difference (MD) for baseline age, severity of dementia and severity of NPS, and the pooled odds ratio (OR) for men, non-White persons, and vascular/mixed dementia with fixed-effects models (Clark, Fairhurst, Cook, & Torgerson, 2015;Ebell, 2013;Trowman et al, 2007). We expected a common effect estimate of zero in these mean baseline variables.…”

“…The baseline imbalances that we investigated were not accounted for in the analyses of all but two trials (Kurlan et al, 2007;Schneider, Tariot, et al, 2006). Our next step was to pool the baseline differences and assess heterogeneity, a method recently developed to quantify baseline differences (Clark et al, 2014(Clark et al, , 2015. None of the pooled baseline differences we studied were statistically significant from zero.…”

Importance of including harms as well as benefits in all clinical trials

“…Christensen et al examined this in 126 trials in 20 systematic reviews of symptomatic treatment of patients with osteoarthritis; patient blinding was of especial concern. Hicks et al took a different approach by applying the method suggested by Clark et al in this journal [2,3] that focusses in baseline heterogeneityeusing a worked example: they removed studies responsible for the heterogeneity until there was zero heterogeneity in the meta-analysis of baseline measurements.…”