Last modified: December 2013

URL: http://cxc.harvard.edu/sherpa/ahelp/calc_mlr.html
Jump to: Description · Example · Bugs · See Also


AHELP for CIAO 4.11 Sherpa v1

calc_mlr

Context: utilities

Synopsis

Calculate the Maximum Likelihood Ratio test

Syntax

calc_mlr(delta_dof, delta_stat)

Description

The calc_mlr command computes significance using the Maximum Likelihood Ratio test using the change in degrees of freedom and the change in the statistic value.

The Maximum Likelihood Ratio (MLR) test is a model comparison test. Model comparison tests are used to select from two competing models that which best describes a particular dataset. A model comparison test statistic, T, is created from the best-fit statistics of each fit; as with all statistics, it is sampled from a probability distribution p(T). The test significance is defined as the integral of p(T) from the observed value of T to infinity. The significance quantifies the probability that one would select the more complex model when in fact the null hypothesis is correct. A standard threshold for selecting the more complex model is significance > 0.05 (the "95% criterion" of statistics).

The MLR test may be used if:


Example

sherpa> calc_mlr(2, 20)

Calculate the maximum likelihood ratio where the change in degrees of freedom is 2 and the change in statistic is 20.


Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

data
copy_data, dataspace1d, dataspace2d, datastack, delete_data, fake, get_axes, get_bkg_plot, get_counts, get_data, get_data_plot, get_dep, get_dims, get_error, get_quality, get_specresp, get_staterror, get_syserror, group, load_ascii, load_data, load_grouping, load_quality, set_data, set_quality, ungroup, unpack_ascii, unpack_data
filtering
get_filter, load_filter, set_filter
info
get_default_id, list_data_ids, list_response_ids
modeling
clean
plotting
plot_data, set_xlinear, set_xlog, set_ylinear, set_ylog
saving
save_error, save_filter, save_grouping, save_quality, save_staterror, save_syserror
utilities
calc_data_sum, calc_data_sum2d, calc_ftest, calc_kcorr, calc_model_sum2d, calc_source_sum2d, get_rate
visualization
contour, contour_data, contour_ratio, get_ratio, get_resid, histogram1d, histogram2d, image_data, rebin