Kazi Mizanur Rahman wrote:
The baseline proportion of a an event was 0.9.
We assume that after providing an intervention in one group for a particular
time period we get the proportion as 0.5. We also have a comparison group
that receives no intervention. After that particular time period the
proportion becomes 0.8 in the comparison group. How to calculate the sample
size with 80% power and alpha .05 ?
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Another possibility is to use the -powercal- package, downloadable from
SSC, which can be used to do power calculations for all generalized linear
models, including the logistic. Information on the methods and formulas
used to do this can be found in Newson (2004). If Kazi does not have access
to the latest Stata Journal in a hurry, then a draft of this can be
downloaded in preprint form from my website at
