are required to estimate a bivariate regression
 model.
 </li>
 <li> Getters for the statistics always compute values based on the current
 set of observations -- i.e., you can get statistics, then add more data
 and get updated statistics without using a new instance.  There is no
 "compute" method that updates all statistics.  Each of the getters performs
 the necessary computations to return the requested statistic.
 </li>
 <li> The intercept term may be suppressed by passing <code>false</code> to
 the <