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<p>Our interest in DAGs relates to a question: should a covariate C be included in a model when the purpose is to study <em>specifically the direct relationship from X to Y</em>? The answer, to be demonstrated experimentally below, is simple.</p>
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<p>If the backdoor pathway is <strong>correlating</strong>, include covariate C to <strong>block</strong> that pathway. On the other hand, if the backdoor pathway is <strong>non-correlating</strong>, incl