Note: This is simply a quick post for those in the know (and more as something for me to look back on to see if I actually know what I’m talking about 😉
Whilst Rank Brain (AI from G) might be the 3rd most important signal at present (after on page and links) within a couple of years I believe it will become the most important.
the score between 1 (dubious) to 10 (very strong) will correlate relevancy.
It clearly closely follows the adwords quality score algo (along with many others e.g. GDN, youTube ads, Gmail Ads, Twitter quality adjusted bids and Facebook Relevancy score). Whilst at present it really only affects long tail queries, after refinement I see this being rolled out across more searches and to head terms (think of how Penguin and Panda got rolled out iteratively).
Put simply; moving forward what people click on (CTR Vs expectation Vs competiton with a smattering of location, day and device type thrown in for good measure) and whether they were satisfied with the result will be extremely important to where a page ranks in the SERPS.
Bottom line: create compelling title tags that not only utilise relevant keywords but also tap into emotion that inspires action. And make sure when people click through you demonstrate to Google that the page is quality in nature e.g. time on site, number of pages visited, on page actions / conversion rates, etc.
Word of warning: Try to game the algo at your peril; Google has been utilising this metric in adwords for 15+ years hence I doubt you will beat it with a bot in the medium-long term.