You didn't understand the parent. See my post below. Also, of course the result could be due to chance. You could flip a fair coin 25 times in a row and come

You didn't understand the parent. See my post below. Also, of course the result could be due to chance. You could flip a fair coin 25 times in a row and come up with heads each time -- it's just pretty damn unlikely. Similarly, I'd bet what he's measured is really this: you have two equally sized groups, one treated, one untreated. In group one you get a rate of x, and in group two, you get a rate of y. How big does |y-x| and the size of the two groups have to be to conclude it was not just chance? As below, a t-test can help you answer that.