Wednesday, May 31, 2017

What does the "Partisan Selective Sharing" study say about PolitiFact?

A recent study called "Partisan Selective Sharing" (hereafter PSS) noted that Twitter users were more likely to share fact checks that aided their own side of the political aisle.


On the other hand, the paper came up in a search we did of scholarly works mentioning "PolitiFact."

The search preview mentioned the University of Minnesota's Eric Ostermeier. So we couldn't resist taking a peek to see how the paper handled the data hinting at PolitiFact's selection bias problem.

The mention of Ostermeier's work was effectively neutral, we're happy to say. And the paper had some surprising value to it.

PSS coded tweets from the "elite three" fact checkers,, PolitiFact and the Washington Post Fact Checker, classifying them as neutral, beneficial to Republicans or beneficial to Democrats.

In our opinion, that's where the study proved briefly interesting:
Preliminary analysis
Fact-checking tweets
42.3% of the 194 fact-check (n=82) tweets posted by the three accounts in October 2012 contained rulings that were advantageous to the Democratic Party (i.e., either positive to Obama or negative to Romney), while 23.7% of them (n=46) were advantageous to the Republican Party (i.e., either positive to Romney or negative to Obama). The remaining 34% (n=66) were neutral, as their statements contained either a contextualized analysis or a neutral anchor.

In addition to the relative advantage of the fact checks, the valence of the fact-checking tweet toward each candidate was also analyzed. Of the 194 fact checks, 34.5% (n=67) were positive toward Obama, 46.9% (n=91) were neutral toward Obama, and 18.6% (n=36) were negative toward Obama. On the other hand, 14.9% (n=29) of the 194 fact checks contained positive valence toward Romney, 53.6% (n=104) were neutral toward Romney, and 31.4% (n=61) were negative valence toward Romney.
Of course, many have no problem interpreting results like these as a strong indication that Republicans lie more than Democrats. And we cheerfully admit the data show consistency with the assumption that Republicans lie more.

Still, if one has some interest in applying the methods of science, on what do we base the hypothesis that Republicans lie more? We cannot base that hypothesis on these data without ruling out the idea that fact-checking journalists lean to the left. And unfortunately for the "Republicans lie more" hypothesis, we have some pretty good data showing that American journalists tend to lean to the left.

Until we have some reasonable argument why left-leaning journalists do not allow their bias to affect their work, the results of studies like PSS give us more evidence that the media (and the mainstream media subset "fact checkers") lean left while they're working.

The "liberal bias" explanation has better evidence than the "Republicans lie more" hypothesis. As PolitiFact tweeted 126 of the total 194 fact check tweets, a healthy share of the blame likely falls on PolitiFact.

We wish the authors of the study, Jieun Shin and Kjerstin Thorson, had separated the three fact checkers in their results.

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