Change the fit statistic in use, for 1 or more spectra.
Syntax: statistic[chi | cstat | lstat | pgstat] [<spectrum range>]
The options are chi-squared (chi) or C statistic (cstat), lstat, or pgstat. If a spectrum number or spectrum range is given, the chosen statistic will only apply to those spectra. It is therefore possible for a multi-spectrum fit to use more than one fit statistic. If no spectrum number or range is given, the chosen statistic will apply to all loaded spectra and will be the default statistic for any future loaded spectra.
Note that the C statistic has a couple of limitations: a) if the calculated model goes to zero in any channel then the format statistic goes to infinity -in practice this is trapped and a large value of the statistic should result; b) the C statistic can be used to estimate parameter values and confidence regions but does not provide a goodness-of-fit. See Arnaud (2003, ApJ submitted) for further details.
Also note that if the chosen statistic is not compatible with the currently used weight method, the weight method will be changed to standard weighting until the conflict is removed.
Examples:
Assume 3 spectra are currently loaded, all using the chi-squared statistic, and that chi-squared is the default statistic.
XSPEC12>statistic cstat 2-3
// Spectrum 1 continues to use chi-sq, 2 and 3 use cstat.
XSPEC12>data 4 spec4.pha
// New spectrum 4 will use chi-sq.
XSPEC12>statistic cstat
// All 4 spectra now use cstat, cstat is the new default.
XSPEC12>data 5 spec5.pha
// New spectrum 5 will use cstat.