So if we have the mean of group 1, the population mean of group 1 minus the population mean of group 2 should be greater than 0. So this is going to be a one-tailed distribution. Or another way we could view it is that the mean of the difference of the distributions, x1 minus x2, is going to be greater than 0. These are equivalent statements. Because we know that this is the same thing as this, which is the same thing as this, which is what I wrote right over here. Now, to do any type of hypothesis test, we have to decide on a level of significance. We have to say, what we're going to do is, we're going to assume that our null hypothesis is correct.