Stat

class sherpa.stats.Stat(name)[source] [edit on github]

Bases: sherpa.utils.NoNewAttributesAfterInit

The base class for calculating a statistic given data and model.

Methods Summary

calc_stat(data, model) Return the statistic value for the data and model.
calc_staterror(data) Return the statistic error values for the data.
goodness_of_fit(statval, dof) Return the reduced statistic and q value.

Methods Documentation

calc_stat(data, model)[source] [edit on github]

Return the statistic value for the data and model.

Parameters:
  • data (a Data or DataSimulFit instance) – The data set, or sets, to use.
  • model (a Model or SimulFitModel instance) – The model expression, or expressions. If a SimulFitModel is given then it must match the number of data sets in the data parameter.
Returns:

statval, fvec – The statistic value and the per-bin “statistic” value.

Return type:

number, array of numbers

calc_staterror(data)[source] [edit on github]

Return the statistic error values for the data.

Parameters:data (scalar or 1D array of numbers) – The data values.
Returns:staterror – The errors for the input data values (matches the data argument).
Return type:scalar or array of numbers
goodness_of_fit(statval, dof)[source] [edit on github]

Return the reduced statistic and q value.

The reduced statisitc is conceptually simple, as it is just statistic / degrees-of-freedom, but it is not meaningful for all statistics, and it is only valid if there are any degrees of freedom.

Parameters:
  • statval (float) – The statistic value. It is assumed to be finite.
  • dof (int) – The number of degrees of freedom, which may be 0 or negative.
Returns:

rstat, qval – The reduced statistic and q value. If the statistic does not support a goodness of fit then the return values are None. If it does then NaN is returned if either the number of degrees of freedom is 0 (or less), or the statistic value is less than 0.

Return type:

float or NaN or None, float or NaN or None