Set the statistical method.
Changes the method used to evaluate the fit statistic, that is the numerical measure that determines how closely the model represents the data.
sherpa.utils.err.ArgumentErr – If the
statargument is not recognized.
The available statistics include:
A maximum likelihood function .
Chi-squared statistic using the supplied error values.
Chi-squared with constant variance computed from the counts data.
Chi-squared with data variance. If the data has 0 counts then the error for that bin is 0.
Chi-squared with gehrels method . This is the default method.
Chi-squared with model amplitude variance.
Chi-squared with data variance to match XSPEC. Errors from zero-count channels (source or background) are ignored if the other channel (background or source) contains counts, or replaced by a minimum value (when both source or background are empty). It should not be used when a model is fit to the background rather than the background is subtracted from the data.
A maximum likelihood function (the XSPEC implementation of the Cash function) . This does not include support for including the background.
A maximum likelihood function which includes the background data as part of the fit (i.e. for when it is not being explicitly modelled) (the XSPEC implementation of the Cash function) .
The least-squares statisic (the error is not used in this statistic).