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 1.
Chi-squared statistic using the supplied error values.
Chi-squared with constant variance computed from the counts data.
Chi-squared with data variance.
Chi-squared with gehrels method 2. This is the default method.
Chi-squared with model amplitude variance.
Chi-squared with data variance (XSPEC-style, variance = 1.0 if data less than or equal to 0.0).
A maximum likelihood function (the XSPEC implementation of the Cash function) 3. 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) 3.
The least-squares statisic (the error is not used in this statistic).
Cash, W. “Parameter estimation in astronomy through application of the likelihood ratio”, ApJ, vol 228, p. 939-947 (1979). http://adsabs.harvard.edu/abs/1979ApJ…228..939C
Gehrels, N. “Confidence limits for small numbers of events in astrophysical data”, ApJ, vol 303, p. 336-346 (1986). http://adsabs.harvard.edu/abs/1986ApJ…303..336G