Binary outcomes
thromboembolic
EVENTS
Results are shown in Difference in estimates from participant-average estimators versus cluster-average estimators and GEEs with exchangeable correlation structures for binary outcomes. Treatment effects are marginal ORs (restrictive versus liberal transfusion strategy), presented with 95% CIs.GEEs: generalised estimating equations; CI: confidence interval; IEEs: independence estimating equations.Estimated using GEEs with an independence working correlation structure with cluster-robust standard errors and equal weight for each patient.Estimated using GEEs with an independence working correlation structure with cluster-robust standard errors and each patient weighted by Estimated using GEEs with an exchangeable working correlation structure with cluster-robust standard errors and equal weight for each patient.The most notable difference was for in-hospital thromboembolic or ischaemic events, where the participant-average OR was 0.43 (95% CI: 0.07 to 2.48) but was almost 25% lower at 0.33 (95% CI: 0.06 to 1.77) for the cluster-average OR. GEEs with an exchangeable correlation structure were similar to the IEE estimate of participant-average effect (odds ratio (OR): 0.41; 95% CI: 0.07 to 2.36).