Does anyone know of any good software for identifying a minimum number of samples needed to obtain, say for example, 80% power at a significance level of 0.05 for a study? Or would you use power tables found online?
Also, if a piece of software/power table says the minimum number of samples is e.g. n=72? Does that mean you only need to test 72 samples? Or does it mean you need to test more than 72 and need to find the effect you're looking for in a minimum of 72 of those samples? Sorry if this sounds waffly - I'm new to this and although I've read around and asked people in my department, no one seems able to point me in the right direction. If anyone has any pointers or ideas for where to look I'd be very grateful!!
Thanks,
Tulip