Immortal Time Bias Found in Many Systematic Reviews, Distorting Results

A new study presented at the 10th Peer Review Congress reveals that immortal time bias (ITB) is widespread in systematic reviews and meta-analyses, significantly affecting effect size estimates and sometimes leading to evidence reversal. ITB occurs when time intervals are misclassified or excluded, creating an erroneous association between exposure and outcome. Researchers assessed the prevalence of this bias in published reviews and quantified its impact, finding that it often inflates or deflates treatment effects. The findings underscore the need for stricter methodological checks in evidence synthesis.