On 23 Lún 2006, at 12:51, Paul Fenner wrote:
I have been asked to analyse the following experiment The outcome
score is a bacterial concentration scored 0 to 5. The data consists
of an initial score, the score after treatment A and then the score
after treatment B. This is measured on 32 subjects. The whole
experiment is then repeated on a new set of 25 subjects but this
time the sequence is initial, treatment B, treatment A. The null
hypothesis is that the removal of bacteria is independent of the
treatment sequence.
I have searched the archive but I cannot find a non-parametric
repeated measures anova. As an alternative I can show, using the
the ranksum test, that there there is no significant difference
between the three measures for the two experiments but I am not
happy with this as it is ignoring the correlated nature of the data
in each experiment.
I have just finished analysing a similar study, with a 5-valued
outcome variable, using ordinal logistic regression and -svy- setting
the data to take account of the multiple measures per participant.
You can specify your analysis of variance model as a regression model
- indeed, if you want a short cut to doing this, run an -anova- in
Stata with the option -regress- and you will see it written as a
regression model. Useful for writing complicated anovas as regressions.
=========
Ronán Conroy
Royal College of Surgeons in Ireland
rconroy@rcsi.ie
+353 (0) 1 402 2431
+353 (0) 87 799 97 95
www.flickr.com/photos/ronanconroy
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