Omitted Variable Bias
Also called: OVB, confounding variable, confounder
Omitted variable bias occurs when a factor that affects the outcome and correlates with your predictor is left out of the model, so its influence is wrongly attributed to what you did include. It's the reason the classic finding that coffee causes heart disease evaporated once smoking was controlled for. Direction and size are predictable from the signs involved, which is why good empirical work argues explicitly about what's missing.
Where this is taught
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