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An effect modifier is a pretreatment covariate such that the magnitude of the treatment effect or its stability changes with the level of the covariate. Generally, other things being equal, larger treatment effects and less heterogeneous treatment effects are less sensitive to unmeasured biases in observational studies. It is known that when there is effect(More)
A frequent concern in making statistical inference for causal effects of a policy or treatment based on observational studies is that there are unmeasured confounding variables. The instrumental variable method is an approach to estimating a causal relationship in the presence of unmeasured confounding variables. A valid instrumental variable needs to be(More)
In medical sciences, statistical analyses based on observational studies are common phenomena. One peril of drawing inferences about the effect of a treatment on subjects using observational studies is the lack of randomized assignment of subjects to the treatment. After adjusting for measured pretreatment covariates, perhaps by matching, a sensitivity(More)
In an observational study of treatment e¤ects, subjects are not randomly assigned to treatment or control, so di¤ering outcomes in treated and control groups may re ‡ect a bias from nonrandom assignment rather than a treatment e¤ect. After adjusting for measured pretreatment covariates, perhaps by matching, a sensitivity analysis determines the magnitude of(More)
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