Chi-square statistic with constant variance computed from the counts data.
In some applications, analysts have seen fit to assume that the
variance is constant for each bin. For this choice of statistic, the
variance is assumed to be the mean number of counts, or
sigma(i)^2 = (1/N) * (sum)_(j=1)^N N(j,S) + [A(S)/A(B)]^2 N(j,B) ,
where N is the number of on-source (and
off-source) bins included in the fit. 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 CVAR
sherpa> SHOW STATISTIC
Statistic: Chi-Squared Constant Variance
- sherpa
-
bayes,
cash,
chidvar,
chigehrels,
chimvar,
chiprimini,
chisquare,
cstat,
get_stat_expr,
statistic,
truncate,
userstat
|
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