Back testing thousands of user queries and comparing them to user click through or satisfaction (clickthrough + dwell)
Thanks, Erik! This is very helpful. What do you mean by 'back testing'?
Also, even without boost links, there seems to be a bias towards popular (long pages). it seems that a focus on # of words in common rather than % is one of the things leading to long articles seeing so much more traction - would this be an easy thing to test as well?