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Covariate

As explained in Causal Inference for Data Science

A covariate is an observed variable included as an input or conditioning variable in a statistical or causal model.

A covariate is an observed variable supplied to a statistical or causal model as an input or conditioning variable. In prediction, covariates such as age and comorbidities define the conditional outcome distribution and help estimate its mean. section 4.1.2

The role changes with the question. A predictive model uses covariates to estimate outcomes, while causal analyses use them to compare more comparable patients or adjust an effect estimate. section 4.1.2 section 5.6

Common uses include:

  • Predicting an outcome conditional on observed characteristics, such as estimating ICU stay from age and comorbidities. section 4.1.2
  • Matching or grouping treated and untreated patients using similar observed characteristics, often through propensity scores. section 5.6
  • Adding variables to a difference-in-differences regression to account for observed differences between groups. section 11.4.5

An added covariate in difference-in-differences

A synthetic dataset adds a variable A to the observed outcomes. The effect estimate is then obtained with a model such as Y ~ D*time_points + A, using A alongside treatment and time. section 11.4.5

How Causal Inference for Data Science covers it

How deep it goes
Defines covariates through regression and conditional expectation, then demonstrates matching and adjustment in causal analyses.
Examples
Uses ICU stay prediction, patient matching, and synthetic difference-in-differences data containing an added variable A.
What you can do after
Apply them via R or Python regression models in a difference-in-differences analysis.
How it connects
Connects covariates to supervised learning, conditional expectation, propensity scores, matching, and difference-in-differences.

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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.