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From | "Nick Cox" <n.j.cox@durham.ac.uk> |
To | <statalist@hsphsun2.harvard.edu> |
Subject | RE: st: Non-normal alternative to MANOVA |
Date | Mon, 5 Jul 2010 12:27:20 +0100 |
This is a frequently asked question without an official FAQ. (It's not StataCorp house style to say "No, we don't do it" unless there is also an explanation of why it is a very bad idea.) See, for example, http://www.stata.com/statalist/archive/2010-05/msg01339.html and several replies. Nick n.j.cox@durham.ac.uk marietherese.kelly@flinders.edu.au Thanks for the replies. I've had a look at transforming the data or using lnskew0, the problem is there are 15 variables, each measured at 3 times periods (baseline, 7 weeks and 3 mothns after treatment) and it's pretty difficult to find a transformation that works for all of them. The data were skewed at baseline and it only got worse after treatment. The confounder numint (number of interventions) is a major issue so I can't ignore it. With 3 repeated measurements I wasn't sure if you could use lnskew0 separately on all 3 of them if I'm interested in changes from baseline? I'll have a look at ranking the data - is there a good reference anywhere on how to do that? I did it once in the past but can't remember the details. > I have been asked to analyse a small dataset from a randomized controlled trial, > with 24 subjects (12 in each group, control and intervention). There are 3 sets > of continuous outcome measures (b1, b2, b3) taken at baseline, 7 weeks and 3 > months, and 2 variables which need to be controlled for - level of impairment > impair (binary) and number of interventions numint (continuous integer). > > If the data were normal I would have done something like this: > > manova b1 b2 b3=group impair numint, continuous(numint) > > and then do various manova tests. > > Unfortunately the outcome data b1-3 are highly skewed, so I can't use manova. > What would be a good alternative? > * * 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/