I'm attempting to calculate n for a trial in medical imaging comparing two different imaging modalities. I've never done this before, so I'm not sure how to approach this and interpret the result.

The outcome for both tests are binary (yes or no). The null is no difference, and the alternative is two sided.

I don't KNOW the expected proportion for each test, but I could read articles about both tests and guess. I do know the prevalence(0.30) of what we are testing for in all subjects.

Should I use: a) pwr.2p.test(h = "guess the effect size", sig.lvl = 0.05, power = 0.8) b) pwr.2p.test(h = ES.h(p1 = "estimate of proportion 1", p2 = "estimate of proportion 2"), sig.level = 0.05, power = .80) c) something else?

I somehow feel like the known prevalence should be included in this...

I'm attempting to calculate n for a trial in medical imaging comparing two different imaging modalities. I've never done this before, so I'm not sure how to approach this and interpret the result.

The outcome for both tests are binary (yes or no). The null is no difference, and the alternative is two sided.

I don't KNOW the expected proportion for each test, but I could read articles about both tests and guess. I do know the prevalence(0.30) of what we are testing for in all subjects.

Should I use:

1. a) pwr.2p.test(h = "guess the effect size", sig.lvl = 0.05, power = 0.8)
2. b) pwr.2p.test(h = ES.h(p1 = "estimate of proportion 1", p2 = "estimate of proportion 2"), sig.level = 0.05, power = .80)
3. c) something else?

I somehow feel like the known prevalence should be included in this...