Hi, I'm doing a study looking at the ability of a test to detect a change in bacterial numbers pre- versus post-treatment [i.e. not treatment effect, but pilot study looking at efficacy of the test used]. I've done a chi-square test and got a significant result (p<0.05). However given that I have a small sample size of 10 patients, is my study considered underpowered? And how do i calculate the ideal sample size for such a study?