specific regression parameters are entered in
<code>mixture</code> separated by <code>+</code>.  By default, an intercept is included.
If no intercept, <code>-1</code> should be the first term included.</p></dd>


<dt id="arg-random">random<a class="anchor" aria-label="anchor" href="#arg-random"></a></dt>
<dd><p>optional one-sided formula for the random-effects in the
linear mixed model. Covariates with a random-effect are separated by
<code>+</code>.  By default, an intercept is included. If no intercept, 