This formula will often underestimate the actual population variance.

该公式通常会低估实际的总体方差。

And we always have to put a little confidence there, because remember, we didn't actually know the population standard deviations, or the population variances.

而且我们总是必须在那里放一点信心， 因为请记住，我们实际上并不知道总体标准偏差或总体方差。

But so, just before we go into the variance of a sample, I think it's instructive to review the variance the population, and we can compare their formulas.

但是，就在我们研究样本的方差之前，我认为回顾一下总体的方差是有指导意义的， 我们可以比较他们的公式。

And one day, I'm going to write a computer program to at least prove it to myself, experimentally, that this is a better estimate of the population variance.

有一天，我将编写一个计算机程序， 至少通过实验向我自己证明， 这是对总体方差的更好估计。

And then this sample variance, calculated this way, will actually underestimate the actual population variance, because they're always going to be closer to their own mean than they are to the population mean.

然后，以这种方式计算出的样本方差实际上会低估实际总体方差，因为它们总是更接近自己的均值，而不是总体均值。

And there's a formula-- and this is actually proven more rigorously than I'll do it-- that is considered to be a better-- or, they'll call it, unbiased-- estimate of the population variance, or the unbiased sample variance.

有一个公式——这实际上被证明比我做的更严格——被认为是更好的——或者，他们称之为无偏——人口方差估计， 或无偏样本方差。