Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
A directed acyclic graph describing a causal structure that could lead to selection bias. In the example in the text, A is coffee consumption, Y is pancreatic cancer, S is selection into the study, C is measured covariates, and U is gastrointestinal disorders.
