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. So you'd probably divide by N minus 1. But let's think about why this estimate would be biased, and why we might want to have an estimate like this that is larger, and then maybe in the future we could have a computer program or something that really makes us feel better that dividing by N minus 1 gives us a better estimate of the true population variance. So let's imagine all of the data in a population, and I'm just going to plot them on a number line. All the data. So this is my number line, this is my number line, and let me plot all of the data points in my population. So this is some data, this is some data, here's some data, and here is some data here, and I can just do as many points as I want.