">+</span> <span class="dv">1</span> <span class="sc">*</span> x[,<span class="dv">1</span>] <span class="sc">*</span> x[,<span class="dv">4</span>] )</span>
<span id="cb2-15"><a href="#cb2-15" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-16"><a href="#cb2-16" aria-hidden="true" tabindex="-1"></a><span class="co"># simulate main effects g(X)</span></span>
<span id="cb2-17"><a href="#cb2-17" aria-hidden="true" tabindex="-1"></a>xbeta <span class="ot">&lt;-</span> <span class="dv">2</span> <span