Hello.
Please bear with me as I am quite inexperienced in statistics.
I want to calculate the power for my experiment, these are the general parameters I used:
n (controls) = 5
n (experimental condition) = 6
average (controls) = 0.000026042
average (experimental condition) = 8.70E-06
pooled standard deviation = 1.5329E-05
I opted for the Mann-Whitney test since I am comparing means from two independent variables which do not follow a normal distribution. Because I have different sample sizes I used the option on top in the calculate effect size menu in G*Power. Thus I used the pooled standard deviation (blue outline) instead of each group's standard deviation.
As you can see I obtained very low power. However, if I use the other option to calculate effect size (the one assuming the same sample size for both groups) I get a much better power value of about 0.97. I have seen guides online in which people use this option even when the sample size of each group is different.
My question: Is it valid to calculate the effect size (and consequently power) in this way, even if the sample sizes are different?
Thank you for your input.