</a>)</span>. For alternative parameterizations, see
section <a href="neg-binom-2-log.html#neg-binom-2-log">negative binomial glm</a>.</p>
<div id="probability-mass-function-9" class="section level3">
<h3><span class="header-section-number">13.1.1</span> Probability Mass Function</h3>
<p>If <span class="math inline">\(\alpha \in \mathbb{R}^+\)</span> and <span class="math inline">\(\beta \in \mathbb{R}^+\)</span>, then for <span class="math inline">\(y \in \mathbb{N}\)</span>, <span class="math display">\[ 