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help for ^robvar^                                            (!!STB-25: sg35.1)
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Robust tests for equality of variance
-------------------------------------

        ^robvar^ varname  [^if^ exp] [^in^ range]^,^ ^by(^groupvar^)^


Description
-----------

^robvar^ calculates three robust tests of the hypothesis that the variance of
a variable is the same across groups.  The ^groupvar^ in the ^by()^ option
defines the groups.  ^robvar^ is a useful supplement to the classical
hypothesis test performed by Stata's ^sdtest^.

^robvar^ reports Levene's statistic (W_0) and two statistics proposed by Brown
and Forsythe that replace the mean in Levene's formula with alternative
location estimators.  The first alternative (W_50) replaces the mean with
the median.  The second alternative replaces the mean with the 10 percent
trimmed mean (W_10).


Option
------

^by(^groupvar^)^ specifies the variable that defines the groups across which
the null hypothesis claims the variance is equal.


Examples
--------

. robvar lgthstay, by(sex)
. robvar lgthstay if age>65, by(sex)

Also see
--------

    STB:  STB-25 sg35, STB-26 sg35.1
 Manual:  [5s] sdtest
On-line:  help for @sdtest@.
