What does "Collider Bias" mean?

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Collider bias occurs when two factors influence a common outcome, and this can lead to incorrect conclusions about the relationship between those factors. Imagine trying to study how two separate causes affect a disease. If you only look at people who have the disease, you may miss important information about how those causes interact.

For example, if we know that both smoking and exercise can lead to heart problems, but we only examine people who have heart problems, we might wrongly assume that exercise has no effect or that it increases risk because we don't see the whole picture. In this case, the disease (heart problems) is acting as a collider, creating a bias in our findings.

Collider bias can skew research results, leading to misunderstandings about how different factors are related. It is important for researchers to be aware of this bias to ensure that their conclusions are accurate and reliable.