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Bias

As explained in Causal Inference for Data Science

Bias is systematic distortion of an estimated effect caused by differences in assignment or other factors associated with the outcome.

Bias is systematic distortion in an estimated effect. In causal analysis, it can arise when treatment assignment differs systematically because of factors also associated with the outcome. section 5.2.1

Choosing a medical treatment

Suppose physicians compare surgery with no surgery using observational data. Age, sex, hospital, radiological findings, and prior illnesses may influence both treatment choice and outcome, making the estimated treatment effect biased. Identifying and adjusting for such confounders can improve the estimate of the average treatment effect. section 5.2.1

Bias can also appear when a time-related event changes the relationship between an outcome and its controls. Predictions of the counterfactual outcome may then reflect those changes rather than the event alone. section 11.3.3

Figure 5.7 Main diagram for this section. C denotes a vector of confounders, T stands for treatment, and O stands for outcome.
figure

A causal diagram links confounders, treatment, and outcome, making the possible route to biased estimates visible. section 5.2.1

How Causal Inference for Data Science covers it

How deep it goes
Explains confounder identification and adjustment, then states how unstable time-series relationships can bias counterfactual estimates.
Examples
Uses physician treatment choices, patient characteristics, hospitals, surgery comparisons, and changing movie-viewing relationships.
What you can do after
Diagnose potential bias by checking confounders and whether control-outcome relationships remain stable around a time-related event.
How it connects
Connects bias with confounders, causal inference, treatment effects, outcomes, counterfactuals, and time series.

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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Causal Inference for Data Science. The section links point to the parts of the book it draws on.