Chi-square statistic with variance computed from data amplitudes.
The chi2xspecvar statistic is equivalent to chi2datavar ("ahelp chi2datavar"), except that when the number of counts in a channel bin is less than 1, the variance is set to 1.
sherpa> set_stat("chi2xspecvar") sherpa> show_stat() Statistic: Chi2XspecVar
Set the fitting statistic and then confirm the new value.
See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.