The Tierney Ratio (sometimes called the Tierney Test because people love alliteration) is a measure of journalistic mediocrity named for its frequent subject, John Tierney. You find the Tierney Ratio of an article by counting the number of words it takes to address all of the significant problems in the article, then dividing that by the article's word count.
As you might expect, Tierney Ratios vary greatly from author to author. The sorely-missed Olivia Judson maintained a TR of virtually zero while writing for the New York Times while John Tierney, a science writer with no appreciable background in or aptitude for science, routinely had observed TRs in excess of one or two. (it is possible that Judson was kept in the Op-Ed rather than Science section out of concern that she would unfairly lower the latter's average.)
The value of the Tierney Ratio is somewhat limited by its serious data censoring problem (analogous to this well-known example). Faced with articles and essays of sufficiently low quality, researchers are almost always forced to leave significant mistakes, distortions and fallacies unaddressed.
Which brings us back to Ray Fisman's recent column in Slate, which reaches an almost Hellmanesque level of inaccuracy. Getting a true TR on something like this is an extraordinarily tedious job so the readers who aren't into hardcore education wonkery might want to skip the next few posts. You'll know it's safe to come back when we start posting Daily Show clips again.