Hernán, Miguel AMonge Corella, Susana2023-06-142023-06-142023-06-07BMJ. 2023 Jun 7;381:1135.http://hdl.handle.net/20.500.12105/16171Effect 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.engVoRhttp://creativecommons.org/licenses/by-nc/4.0/Selection BiasHumansBiasAtribución-NoComercial 4.0 Internacional37286200381113510.1136/bmj.p11351756-1833BMJ (Clinical research ed.)open access