de>+</code> symbol which stands for the English word “and” rather than an sum in the arithmetic sense. </p><div class="no-row-height column-margin column-container"><span class="margin-aside">Occasionally, we will use the <code>*</code> symbol instead of <code>+</code> for reasons that will be pointed out whenever we come to such a situation. We will also sometimes use mathematical functions such as <code>log()</code> or <code>ns()</code> in the model specification.</span></div></div>
<p>From time to ti