问题：uber不同算法 - 选event还是user based？

metric sensitivity and robustness

- average is sensitive to outliers

- easy to move? (median is hard to change)

- standard deviation vary a lot?

Normal Distribution Steps - confidence interval

1. calculate p difference

2. calculate p pool

3. calculate pool standard deviation (if given empirical sd, use new sd/se)

4. calculate margin of error

5. calculate confidence interval

6. check statistical (default is 0)/practical (if given dmin) significance

问题：为什么smoking那道题normal distribution的顶是20%？不是10000人里有8000人抽烟吗

analytical variability - 通过ab测试的实验数据得出，容易underestimate （不复杂的normal distribution用这个）

如何计算：1. 算difference 2. p pool 3. SE_pool 4. margin of error 5. confidence interval

empirical variability - 通过以前的实验或者理论得出，适用于non-parametric metric

如何计算：1. 求difference 2. 用diff算stdv

问题：课最后的diff order怎么得出来的