They’re obvious, but they’re not obviously right. All those assumptions that you mention above have to be tested. And every time you throw in another factor t

They’re obvious, but they’re not obviously right. All those assumptions that you mention above have to be tested. And every time you throw in another factor to consider, you need to test on a larger sample size to get a valid and reliable model. Look, I’ve worked in the search-engine biz for over five years, and while I myself haven’t gone beyond stats 101, some of my co-workers have studied this stuff at the grad-school level, and they are constantly arguing with one another about how to measure the “quality” of a search engine, and then, given that measurement, what particular kind of statistical model to use in order to predict, given a query and a bunch of potential results, which result has the highest “quality”. (Note that in the particular subfield of search that we are working with, spam pages and black-hat SEO are not really concerns.) And we (like Google and everyone else in this industry) have the luxury of trolling through millions of clicks’ worth of log files and we can hire semi-skilled labor to train our statistical models. And compared with measuring the “quality” of a teacher in a classroom, measuring the “quality” of a search engine is trivially easy.