To answer your question, editors decide what to publish based on their judgments and not on a some formula. Basically, whatever they believe is newsworthy (the above list is a good guide). The content is based on several factors: the readers or viewers that make up their market, space available for news, the editors’ own judgments, the feedback the media outlet receives from meetings with readers and focus groups, and so on. One thing I like to do is compare the first 15 minutes of the 6pm news among the two main stations as well as the front page news (or whatever section is of interest) of our two major dailies in Vancouver and nationally. It gives me a good sense of the kinds of stories covered and helps me better understand how editors’ (and different media outlets) prioritize news.