Use this free bayesian A/B testing calculator to find out if your test results are statistically significant.

Use this free bayesian A/B testing calculator to find out if your test results are statistically significant. 
https://marketing.dynamicyield.com/bayesian-calculator/

Learning to rank problems. Well explained

Learn to rank and its various optimizations - http://opensourceconnections.com/blog/2017/08/03/search-as-machine-learning-prob/

http://opensourceconnections.com/blog/2017/04/01/learning-to-rank-linear-models/

What works in e-commerce - a meta-analysis of 6700 online experiments

http://www.qubit.com/sites/default/files/pdf/qubit_meta_analysis.pdf