Chi-square statistic with variance computed from the data.
If the number of counts in each bin is large (> 5), then the shape
of the Poisson distribution from which the counts are sampled tends
asymptotically towards that of a Gaussian distribution, with variance
sigma(i)^2 = N(i,S) + [A(S)/A(B)]^2 N(i,B) .
The background term appears only if a background region is specified
and background subtraction is done.
See
CHISQUARE
for more information, including definitions of the quantities shown above.
Specify the fitting statistic and then confirm it has been set.
sherpa> STATISTIC CHI DVAR
sherpa> SHOW STATISTIC
Statistic: Chi-Squared Data Variance
- sherpa
-
bayes,
cash,
chicvar,
chigehrels,
chimvar,
chiprimini,
chisquare,
cstat,
get_stat_expr,
statistic,
truncate,
userstat
|
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