d>
<dt><code>rad</code></dt><dd>
<p>index of accessibility to radial highways.
</p>
</dd>
<dt><code>tax</code></dt><dd>
<p>full-value property-tax rate per $10,000.
</p>
</dd>
<dt><code>ptratio</code></dt><dd>
<p>pupil-teacher ratio by town.
</p>
</dd>
<dt><code>black</code></dt><dd>
<p><code class="reqn">1000(Bk - 0.63)^2</code> where <code class="reqn">Bk</code> is the proportion of blacks
by town.
</p>
</dd>
<dt><code>lstat</code></dt><dd>
<p>lower status of the population (percent).
</p>
</dd>
<dt><code