I need to calculate the sample size for a study with the primary objective being to test the efficacy of a new treatment. The failure rate of the existing treatment is only 5%...

the developer claims that the new treatment will have a failure rate of not more than 2%, perhaps even 1%. However, if I use proportions difference, the difference is 3%-4%, which yields a sample size of hundreds if not thousands of patients to be examined. This is not practical.

I read that there are ways of reducing the sample size, by changing the question, for example, by using ratios or odds ratios instead of differences, however I am not sure I understand why.

If I use ratios, then not only that I need the sample size formula, I also need to know how to analyze it later (the regular hypothesis testing for proportion diff won't work)

thanks...