"Proving", in this case, is whether the performance of one title is better than another at statistically significant level. Performance can be faceted by refer

"Proving", in this case, is whether the performance of one title is better than another at statistically significant level. Performance can be faceted by referrer if necessary if there's a need to control the results further, or exclude sources where title A/B testing can't feasibly be done or has noticeably different behavior. (an example is using a different title for social sharing vs. the article title itself) This is generally how title A/B testing works at every major online publisher.