lity</code> causal link is only one of the <em>pathways</em> between <code>drug</code> and <code>mortality</code>. The other pathway is <code>drug</code><span class="math inline">\(\leftarrow\)</span><code>health</code><span class="math inline">\(\rightarrow\)</span><code>motality</code>. When we model <code>mortality ~ drug</code>, will we be studying just the direct link, or will the other pathway get involved? This is the sort of question we will address in this Lesson, as well as how to <em>block</em> a