Prevalence of survivor bias in observational studies on fresh frozen plasma:erythrocyte ratios in trauma requiring massive transfusion.

In this very interesting paper, Ho et al. assess the importance of survival bias in massive transfusion studies. Indeed, although the evidence for the use of high FFP:RBC ratios is increasing, it is supported mainly by uncontrolled observational studies that suffer from missing data and analytical biases. The most important one is the survival bias because those who survive longer are more likely to receive plasma transfusion versus patients who die early after admission. This bias could influence statistical analyses.

The authors analyzed 26 studies on blood ratios in trauma: eleven studies were judged survivor bias-prone, favoring a higher ratio. Fifteen were survivor bias-unlikely or biased against a higher ratio; among them, 10 showed an association between a higher ratio and improved survival, and five did not. How can we conclude?

This analysis demonstrates that survival bias is common in published trauma studies. It underlines the urgent need for randomized controlled trials. We are awaiting their results.

– Anne Godier