Bmc Med Res Methodol
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The counterfactual or potential outcome model has become increasingly standard for causal inference in epidemiological and medical studies. ⋯ Counterfactuals are the basis of causal inference in medicine and epidemiology. Nevertheless, the estimation of counterfactual differences pose several difficulties, primarily in observational studies. These problems, however, reflect fundamental barriers only when learning from observations, and this does not invalidate the counterfactual concept.