I recently wrote a column for Columbia Journalism Review based on my field experiment with Jason Reifler testing the effectiveness of fact-checking on state legislators. Here’s how it begins:

Factcheckers often struggle to change the minds of skeptical voters. But what effect do they have on the politicians under scrutiny? Can the threat of being factchecked help keep politicians honest?

To answer this question, my co-author Jason Reifler of the University of Exeter and I conducted a field experiment during the final months of the 2012 campaign. We sent letters to hundreds of state legislators in the states where PolitiFact has an affiliate warning of the potential electoral and reputational consequences of negative factchecks. The results of our study, which we announced this week in a Politico op-ed and New America Foundation report, were striking: lawmakers who were sent the letter about the threat posed by factchecking were significantly less likely to have their statements publicly questioned as inaccurate by factcheckers or other sources than those who were not.

Our findings suggest that the presence of factcheckers creates a watchdog effect, helping to constrain politicians by increasing the costs of inaccuracy. But they also have implications for how factchecking outlets and the funders who support them allocate their resources. We believe factcheckers should broaden their focus beyond the presidential campaigns and national political figures who now receive the overwhelming majority of their attention, especially during elections.