- #1
imsmooth
- 152
- 13
Maybe someone is really good with stats, or has access to a statistics professor. Here we go:
I am trying to determine the power for a study. The distribution is binomial. I have a device that either works or does not work. I do not know the real probability, but I think it is very good. Let's assume p = 0.75. I am going to try it 50 times. Using a binomial distrtibution program I determine that if I get 43 or more successes, this will happen by chance less than 5% (p = 0.05) of the time. So, I will accept that the device works at least 75% of the time if I get 43 successes or more. The question then is what is the power of this study? This seems to be predicated on the fact that I know the real probablility. If I think the device works 89% of the time I find that my power is 82%. If the true success rate is 90% the power goes up to 87%.
How can I get a meaningful number for the power? If my effect size is large, true I have a larger power. But, I don't know the real effect size. I can make the power of the test arbitrarily large by just stating I have large effect size. This does not seem right.
I am trying to determine the power for a study. The distribution is binomial. I have a device that either works or does not work. I do not know the real probability, but I think it is very good. Let's assume p = 0.75. I am going to try it 50 times. Using a binomial distrtibution program I determine that if I get 43 or more successes, this will happen by chance less than 5% (p = 0.05) of the time. So, I will accept that the device works at least 75% of the time if I get 43 successes or more. The question then is what is the power of this study? This seems to be predicated on the fact that I know the real probablility. If I think the device works 89% of the time I find that my power is 82%. If the true success rate is 90% the power goes up to 87%.
How can I get a meaningful number for the power? If my effect size is large, true I have a larger power. But, I don't know the real effect size. I can make the power of the test arbitrarily large by just stating I have large effect size. This does not seem right.