What I would be interested in knowing is what metrics Google uses to optimize their systems. When rolling out a new update do they only look at click through ra

What I would be interested in knowing is what metrics Google uses to optimize their systems. When rolling out a new update do they only look at click through rates ? Do they have human moderators rate a sample of search results ? Given the large number of people such ranking algorithms affect I foresee regulations being passed to make them more transparent. Companies should be required to publish audits about whether their algorithms are biased towards protected categories and other things like their competitors or big companies.