I'm no authority, but there is a small section in Van Belle's
"Statistical Rules of Thumb" that discusses sample size calculations in
terms of relative changes, e.g. percent. Van Belle frames the sample
size calculation in terms of 'proportionate change in means' and
'coefficient of variation' which would require a percent expression of
the variability. If possible, you may want to consider reading Van
Belle's discussion on this topic.
--Clint
>>> ovaldia@yahoo.com 9/29/2004 12:04:04 PM >>>
Dear all,
In an article that I am reading the authors write:
"it was decided a priori to include a minimum quantity
of mother, which could allow the statistical power
(alpha=0.05, beta=0.80) for assessing
differences of 10% in nicotine concentration by group
with an expected standard deviation of 15 ng/mg. These
criteria led to the analysis of 150 mothers (50 for
each of the 3 groups)"
They claim that they did this and all analysis using
Stata 5.0. They do not provide group means or any
discriptive statistics on which the sample size was
computed.
Can someone please tell me how this could have been
done. And is there a program to do this in Stata?
Thank you in advance,
Ricardo
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