Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Jun 7:381:1135.
doi: 10.1136/bmj.p1135.

Selection bias due to conditioning on a collider

Miguel A Hernán  1 , Susana Monge  2   3
Affiliations

Selection bias due to conditioning on a collider

Miguel A Hernán et al. BMJ. .

Abstract

Effect estimates may be biased when the study design or the data analysis is conditional on a collider—a variable that is caused by two other variables. Causal directed acyclic graphs are a helpful tool to identify colliders that may introduce selection bias in observational research.

PubMed Disclaimer

Figures

Fig 1
Fig 1
Three types of causal graphs. I=infection; J=fourth variable; S=susceptibility to infection; V=vaccine
See this image and copyright information in PMC

References

    1. Pearl J. Causality. Cambridge University Press, 2009. 10.1017/CBO9780511803161. - DOI
    1. Greenland S, Pearl J, Robins JM. Causal diagrams for epidemiologic research. Epidemiology 1999;10:37-48. 10.1097/00001648-199901000-00008 - DOI - PubMed
    1. Hernán MA, Hernández-Díaz S, Robins JM. A structural approach to selection bias. Epidemiology 2004;15:615-25. 10.1097/01.ede.0000135174.63482.43 - DOI - PubMed
    1. Monge S, Pastor-Barriuso R, Hernán MA. The imprinting effect of covid-19 vaccines: an expected selection bias in observational studies. BMJ 2023;381:e074404. - PubMed
    1. Chemaitelly H, Ayoub HH, Tang P, et al. . COVID-19 primary series and booster vaccination and immune imprinting. medRxiv 2022;2022.10.31.22281756 10.1101/2022.10.31.22281756. - DOI

LinkOut - more resources