Funnel plot of Chlamydia pneumoniae DNA detection (Review Manager 4.04). Precision of estimate (reciprocal of standard error) versus odds ratio for studies of circulating C. pneumoniae DNA detection by cardiovascular disease status compared with disease-free controls. The dotted line indicates the pooled odds ratio of the studies at 2.0. The curve illustrates a funnel plot centred about the most precise study, in which an equal number of studies are expected in the left and right tails. Asymmetry of the funnel plot suggests publication bias, or bias in selection of cases or controls.