So the sampling distribution of this statistic, p1 minus p2. Now what's the standard deviation of the distribution going to be? In the last video, we figured out that we could represent it by this formula over here. But with our null hypothesis, we're assuming that p1 and p2 are the same value. So let me rewrite it. So in our last video, and I don't want to confuse the issue, because in the last video I made this approximation over here. So let me write the clean version down here.