Well, in the last video we talked about that if we want to have an unbiased estimate, and here in this video I want to give you a sense of the intuition why, we would take the sum, so we're going to go through every data point in our sample, we're going to take that data point, subtract from it the sample mean, square that, but instead of dividing by N, we divide by N minus 1. We're dividing by a smaller number. And when you divide by a smaller number, you're going to get a larger value. So this is going to be larger, this is going to be larger, this is going to be smaller. And this one we refer to the unbiased estimate. And this one we refer to the biased estimate. If people just write this, they're talking about the sample variance, it's a good idea to clarify which one they're talking about, but if you had to guess and people give you no further information, they're probably talking about the unbiased estimate of the variance.