

<h3>Source</h3>

<p>Pinheiro, J. C. and Bates, D. M. (2000), <em>Mixed-Effects Models in S
and S-PLUS</em>, Springer, New York.  (Appendix A.8)
</p>
<p>Davidian, M. and Giltinan, D. M. (1995), <em>Nonlinear Models for
Repeated Measurement Data</em>,  Chapman and Hall, London.
</p>
<p>Joyner and Boore (1981), Peak horizontal acceleration and velocity from
strong-motion records including records from the 1979 Imperial
Valley, California, earthquake, <em>Bulletin of the Seismological
Society of America</em>,