One is when we are dealing with proportions. So I'll write that on the left side right over here. And the other is when we are dealing with means. In the proportion case, when we're doing our significance test, we will set up some null hypothesis that usually deals with the population proportion. We might say it is equal to some value. Let's just call that P sub one. And then maybe you have an alternative hypothesis that well, no, the population proportion is greater than that or less than that or it's just not equal to that.