PolitiFact and lessons unlearned: the "Truth Index"

PolitiFact continues to focus on marketing at the expense of quality, with the rollout of the "Truth Index" serving as the latest example.

PolitiFact's description (by editor Bill Adair):

An average of all Truth-O-Meter rulings

To calculate the Index, we use the Truth-O-Meter ratings from our national and state sites for the prior seven days. We chose seven days to get a larger sample and avoid the dramatic swings that would occur if it were based on one day.

It's hard to imagine that even if PolitiFact controlled for selection bias that the "Truth Index" would carry any value at all other than entertainment.  Is the index supposed to show trends in the truthfulness of politicians and others who receive the PolitiFact treatment?  Again, even given appropriate controls on the selection of statements, the index probably means absolutely nothing in terms of daily trends.  We might hypothesize that as politicians increase their awareness of the popularity of fact checking sites that they would develop a less cavalier attitude toward their political speech.  But that isn't something that one would measure from day to day with a running average, even one softened using a period of seven days.

In terms of fact checking, the "Truth Index" is nonsense.  In terms of marketing perhaps it makes sense.

This is why I call PolitiFact the Fox News of fact checking:  They favor style over substance in search of ratings.