Although Joseph as always gives good advice, it is also arguable that if
a structure of groups and of individuals within groups is key, then any
test like this is misdirected. It is difficult to advise without knowing
much more about the data.
Nick
[email protected]
Joseph Coveney
If you have ties in your response variable, then you'd be better off
using the
with-ties p-value. You can check for ties with the Stata command
-isid-.
sysuse census
kwallis medage, by(region)
isid medage
If you're interested in within-person comparisons, then there's
Friedman's test;
there are user-written commands, e.g., -friedman- and -skilmack-. For
between-groups testing where there are multiple observations on each
person,
there is van Elteren's test (two groups at a time), again, with a
user-written
command, -vanelteren-. Another user-written command that could be
helpful in
your case is -somersd-, which allows for a -cluster()- option. All of
these can
be downloaded from SSC (-help ssc- for how). You can try -permute- with
a
randomized-block ANOVA, too. As I recall, there's a worked example in
the
documentation for -permute-, which is an official Stata command.
"a statistical test for medians"--many nonparametric tests are tests of
location
only when the scale is the same between groups.
Mahboobeh Safaeian wrote:
I am using the Kruskal Wallis rank test to see if there are any
statistically
significant differences in 3 different groups. I have 2 questions
(unrelated):
1) How do I determine whether I use the p-values with ties or without
ties?
2) is there a statistical test for medians that can account for multiple
observations per person (kind of like a GEE)?
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