# Sample size calculation for study aiming to demonstrate non-inferiority of a drug

I need to calculate the sample size required for an observational study in which incidence of disease is 19-29%. Population affected is 600,000 people.

The study has two samples similar on baseline characteristics treated with two different drugs.

Statistical analysis will be chi-square and Fisher's test. I have to demonstrate non-inferiority of one drugs with respect of the other one. I don't have any other info.

Can anyone help me to calculate the sample sizes required in order to obtain power of 0.80 with an alpha 0.05?

• Surely one of the applets at statpages.org/#Power will solve your problem.
– whuber
Commented Dec 14, 2010 at 18:35
• @Roland How could you compute a sample size in a power study from a non-inferiority trial if you don't know the expected difference (or equivalently, the % of patients responding to the new treatment compared to the actual one)?
– chl
Commented Dec 15, 2010 at 20:35