- I have a treatment that I know to be effective, but I want to determine precisely how effective it in a (large) group of individuals
- I'm dividing them in to a test group and a control group so I can compare the effect of the treatment
- However, I want to keep the test group as large as possible (so as many people as possible get the treatment) and the control as small as possible, while still being able to determine how effective the treatment is with some confidence
- With other (unrelated) tests in the past, we have arbitrarily used an 80/20 test control split, but we now want to try to make our tests more effective by keeping the control group as small as possible

What approach can I use to determine this?

Thanks