The company that carried out the analysis flagged all classrooms that showed a number of wrong-to-right erasures exceeding three standard deviations from the mean.
进行这次分析的公司给所有班级做了标记，这些班级存在大量不符合三个与意思偏离标准的错改对的现象。
2
If you do this, you find the the expected frequency is 0 because deviations from a mean always sum to 0.
如果您这么做，您会发现期望频率是0，因为平均值的偏差的和永远是0。
3
Even small deviations in growth rates can mean hundreds of billions or even trillions of dollars in the federal budget deficit.