When I have a binary outcome variable and a binary predictor, I am able to calculate the sample size needed using either G*Power (under z tests -- logistic regression) or R (wp.logistic). However, I do not know how to tackle this when the predictor variable has three groups/categories. Does anyone know how to go about these calculations, and using what software? Thanks in advance.
@Robin refer to the below mentioned manuscript.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6422534/#:~:text=A%20simple%20formula%20such%20as,the%20accuracy%20of%20the%20statistics.
Thanks Imran, but I'm looking to calculate the sample size needed rather than go by 'rules of thumb'. Any suggestions?
There are a few online calculators for this just google the topic. Most people recommend doing it by simulation. See the attached search for references. Best wishes, David Booth
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