I am currently reading Math behind A/B testing written by Amazon and got stuck. At some point they say:
To determine the 95% confidence interval on each side of conversion rate, we multiply the standard error with the 95th percentile (one tailed) of a standard normal distribution (a constant value equal to 1.65).
Then they use that constant to calculate the confidence interval:
range = conversion rate +- (1.65 x Standard Error)
I read somewhere to get the aforementioned constant value from the following table:
The problem is that I can't see
1.65 anywhere for
95% and the closest value is
1.960, hence my confusion.
Could someone explain me where the
1.65 is coming from?