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.

I’ve argued before that journalistic factchecking probably helps to constrain even national politicians in the manner we propose. The stream of half-truths and dissembling we see today may be frustrating, but contrary to the laments from many commentators, it’s hard to believe that there wouldn’t be more misleading claims in an otherwise identical world with no factcheckers (Neil Newhouse’s protestations notwithstanding).

Still, it is likely that factchecking has relatively modest effects on the behavior of presidential campaigns and national leaders, who already receive a vast amount of coverage and often wield substantial advertising budgets. One additional negative article is unlikely to make much of a difference to their reputations or careers. In addition, the people who follow national politics closely enough to know or care about factchecks have largely made up their minds about the candidates and officials in question. In this sense, the readers of factchecks are typically more like fans of a sports team than readers of Consumer Reports, a mindset that helps produce the motivated resistance to corrective information that Reifler and I have observed in our research.

Additional factchecking in state and local politics, by contrast, should have more significant effects. First, members of the public know less about the candidates and officials in question and are less likely to be polarized in their opinions. In addition, these officials receive much lower levels of coverage and often have few resources available to get their message out. As a result, additional scrutiny from factcheckers poses a relatively greater threat to their prospects for re-election (a domain in which previous research suggests that officials are highly risk-averse). It also poses a greater threat to legislators’ reputations, which could influence their future hopes of entering leadership or running for higher office.

Brendan Nyhan is an assistant professor of government at Dartmouth College. He blogs at brendan-nyhan.com and tweets @BrendanNyhan.