Meta-analyses: how to read a funnel plot

Researchers undertook a meta-analysis to evaluate the relative short term safety of carotid endarterectomy compared with carotid artery stenting.1 Randomised controlled trials were included if they compared carotid endarterectomy with carotid artery stenting in patients with carotid artery stenosis (with or without symptoms). In total, 10 trials were identified that reported short term outcomes. The primary endpoint was mortality or stroke within 30 days of the procedure. The total overall periprocedural risk of mortality or stroke was lower for carotid endarterectomy than for carotid artery stenting (odds ratio 0.67, 95% confidence interval 0.47 to 0.95; P=0.025). A funnel plot was presented (figure⇓). Egger’s test gave a P value equal to 0.932. Funnel plot for the meta-analysis of the short term safety (periprocedural mortality or stroke) of carotid endarterectomy compared with carotid artery stenting Which of the following statements, if any, are true? Statements a and b are true, whereas c is false. The meta-analysis investigated the relative short term safety of carotid endarterectomy compared with carotid artery stenting. Ten trials were identified …