I'm doing a study on comparing the prevalence and severity of extrapyramidal side effects between patients with schizophrenia who smoke tobacco and who don't.
How can I determine the sample sizes for each group?
Here you can find an online calculator of the sample size for different study designs. You need to know what alpha risk you can take, what beta risk, and what proportions in both subsamples — or what difference — do you think you should compare (based on what you find in the scientific literature, and the goals of your study) .