Your best bet is to go to a scientific journal – probably of a biological nature. They often report results of testing the efficacy or difference of something and usually have means of 2 or more groups estimated from a sample and employ confidence intervals. A problem may be getting access. Some only allow paid members to see the publications. I would google "American Journal of ______" and put just about any biological term where I drew the line. This will eventually get you to a journal you can view. I would pick a subject that you are most familiar with. If I can be of further assistance please ask and thank you for the question.

Also, you might be able to find articles in libraries that have scientific journals.

Try going to "www.sciencedirect.com" to find an article.

I believe that "sciencedirect.com" may charge for papers so you might want to try the other approaches first.