And so a very easy rule of thumb is calculate this quantity either way. Calculate this quantity either way. If you have more than 30 samples, if your sample size is more than 30, your sample standard deviation is going to be a good approximator for your population standard deviation, and so this whole thing is going to be approximately normally distributed. And so you can use a z table to figure out the probability of getting a result at least that extreme. If your sample size is small, then this statistic, this quantity, this is going to have a t distribution. And then you're going to have to use a t table to figure out the probability of getting a t value at least this extreme. And we're going to see this in an example a couple of videos from now.