a/b test, confidence level

gistfile1.md

http://20bits.com/articles/hypothesis-testing-the-basics/

http://20bits.com/articles/an-introduction-to-ab-testing/

http://20bits.com/article/statistical-analysis-and-ab-testing

awk: http://www.grymoire.com/Unix/Awk.html#uh-18

http://mathworld.wolfram.com/NormalDistribution.html

http://stackoverflow.com/questions/809362/cumulative-normal-distribution-in-python

=== binomial test

http://elderlab.yorku.ca/~aaron/Stats2022/BinomialTest.htm