 estimate it, because very
low variances create problems with  numerical evaluation. In these cases, consider estimating without that random effect.</p></li>
<li><p>The model is estimated by maximum likelihood estimation.</p></li>
<li><p>Non-linear models may have up to 3 nested levels.</p></li>
<li><p>To choose the number of quadrature points for non-linear model evaluation, a balance is needed between accuracy and
speed; estimation time increases quadratically with the number of points chosen. In addition