If Yelp wanted to understand if ratings helped users pick a listing, and we use the CTR as the success metric to run the ab test, how do we know that a significant change in CTR is due to just the ratings and not other parts of the listing like the reviews?
Do we have to do some kind of user segmentation instead of randomly assigning users before running the ab test?
Randomization takes care of all other variables but the treatment. Test on statistical significance takes care of the choice between the treatment and chance. It's only when you can't do a randomized trial, that you need to control for other differentiators.