The 2 sigma comes from two standard deviation, sigma, the symbol for standard deviation.

2 sigma 来自两个均方差，sigma 是均方差的符号。

Readers have to wait until page 65 before reaching the first serious concept, standard deviation, which feels too late.

读者得等上65页才能接触到第一个严肃的统计学概念——标准差，让人感觉进度太慢。

The critical variable was the standard deviation of the means divided by the mean of the standard deviations.

关键变量是均值的标准差除以标准差的均值。

Let's say 2.79 is the standard deviation.

设2.79是标准偏差。

And the standard deviation is 0.5.

标准偏差 0.5。

Do you know how to calculate the standard deviation ?

道如何计算标准差吗？

What if we got two standard deviations more conscientious?

如果我们得到两个更认真的标准差呢？

The calculated standard deviation of the data in Table 2 is 12.14 .

表2中数据的计算标准差12.14。

Raymond, you were the one who scored one standard deviation higher than Debra.

雷蒙德，的成绩应该比黛布拉高一个等级。

So based on the data given for this population, and using the standard deviation formula, what do you think this variable is?

以这个人口数据基础再用标准差公式，觉得变量是多少？

Table 4 compares the percentages based on using the standard deviation and the variances.

表 4 比较了基于标准差和方差的百分比。

So, you know M for mean,   as for standard deviation but both in Greek.

所以，道 M 代表平均值，M 代表标准差，但两者都是希腊语。

So it's going to have a smaller standard deviation.

所以它的标准偏差会更小。

Which basically just rescales the units so that the standard  deviation of our expression will equal one.

这基本上只是重新调整单位，使我们的表达式的标准差等于 1。

So we go down another standard deviation in that direction and another standard deviation above the mean.

所以我们在那个方向上再下降一个标准差，在平均值之上再下降一个标准差。

Now if we're talking about two standard deviations around the mean-- so if we go down another standard deviation.

现在，如果我们谈论均值附近的两个标准差——那么如果我们再下降一个标准差。

And if you take its square root for the standard deviation, which is what we do right here, it's 0.49.

如果用它的平方根来表示标准偏差，这就是我们在这里所做的， 它是 0. 49。

So we know our sample standard deviation is 1.04.

所以我们道我们的样本标准差是 1.04。

DUCKWORTH: So, we've not only gotten smarter, we've become two standard deviations smarter than we were 100 years ago.

DUCKWORTH：所以，我们不仅变得更聪明了，而且比 100 年前更聪明了两个标准差。

The total variation is based on the standard deviation.

总变异基于标准差。