Nonparametric tests tend to lose a lot of power when you have many ties as you will have here.
You may benefit from a model for discete ordinal data such as -ologit-. However it is not set up for repeated measures analysis. You may find -gllamm- helpful there. See http://gllamm.org.
-----Original Message-----
From: "Yupa" <[email protected]>
To: "Statalist" <[email protected]>
Sent: 7/25/2008 6:04 PM
Subject: st: Statistical advice about multiple comparison...
Dear statalisters,
I have 9 test items and each item is scored ordinally 1 to 4 points
(distance between points isn't equal).
The test is administered to two populations; in the first population
each item is taken two times for each subject (at different ages). The
second population served as reference.
Some of the test items show a ceiling effect (aren't able to
discriminate at high end of the scale, and lower scores are not
represented).
I have to compare the results of each item between the two timepoints of
the first population and between each timepoint of the first population
versus the reference population.
I think that an equality test for matched data is adequate for the first
comparison (signrank) and an equality test for unmatched data (ranksum)
for the second.
Am I right or am I missing something?
May I analyze the data in a different way (different tests)?
Thanks in advance!
Francesco
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
