When Republican Scott Brown faced Democrat Martha Coakley in a January 2010 special election for Ted Kennedy’s Senate seat, he was criticized by Coakley and other Democrats as being too conservative. But was he really a conservative at all?

Media coverage at the time frequently bought into the claim that Brown was a conservative, which coincided with some of the themes of his campaign and the wave of grassroots support it attracted on the right. Glen Johnson’s report for The Associated Press on Brown’s victory in the Republican primary, for instance, stated that Brown had “carved out a decidedly conservative record.” Similarly, he was labeled as conservative in reports from Slate’s Christopher Beam, the UPI wire service, and Roll Call’s Byron C. Tau, among others—including CJR.

But Boris Shor, a political scientist at the University of Chicago’s Harris School of Public Policy Studies, came to a different conclusion in the days before the Massachusetts special election. Drawing on ideological estimates from his research with Princeton’s Nolan McCarty, Shor noted that Brown is a “liberal even in his own party,” which leans further left than Republicans in almost any other state:

Brown’s [ideological] score puts him at the 34th percentile of his party in Massachusetts over the 1995-2006 time period. In other words, two thirds of other Massachusetts Republican state legislators were more conservative than he was. This is evidence for my claim that he’s a liberal even in his own party. What’s remarkable about this is the fact that Massachusetts Republicans are the most, or nearly the most, liberal Republicans in the entire country!

In a follow-up post after Brown’s victory, Shor forecast that Brown would be the most liberal Republican in the Senate. That prediction turned out to be close to the mark. Contrary to media descriptions during his campaign, Brown ended up as the third-most liberal Republican senator during his time in Congress, according to estimates from the political scientists Keith Poole and Howard Rosenthal, falling just to the right of Maine’s Olympia Snowe and Susan Collins. [Disclosure: Shor is currently a Robert Wood Johnson Scholar in Health Policy Research at the University of California, Berkeley/University of California, San Francisco. I served as an RWJ scholar at the University of Michigan from 2009-2011.]

The fact that many reporters dubbed Brown a conservative during his Senate run is not surprising given some of his positions and rhetoric. One of the challenges of state-level political reporting is the lack of easily accessible information on the voting records and ideological positions of lawmakers, which makes it harder for journalists to scrutinize the way candidates like Brown define themselves.

Now, however, that information is easier to come by. On Monday, Shor and McCarty made their state legislator ideological estimates for the 1993-2011 period publicly available for the first time, along with chamber-level estimates of state legislative polarization. These data are a valuable resource for statehouse journalists with numerous potential applications in both legislative and campaign reporting.

For an example of how ideological estimates can be incorporated into political reporting, consider the work of Milwaukee Journal-Sentinel reporter Craig Gilbert. As I showed in a piece dubbing him the “most political science-friendly reporter in America,” Gilbert used Poole and Rosenthal’s data to explain the ideological stakes in Wisconsin’s 2012 U.S. Senate race and to compare levels of polarization by party in the state’s Congressional delegation.

A similar approach can be employed with Shor and McCarty’s data, as Shor’s blog posts on recent political events illustrate. For instance, their aggregate state-level data can be used to assess the relative positions of the parties across states and to compare the relative polarization between the two major parties, as Shor did in making this figure yesterday:

The data are already available in Google Public Data Explorer and can be used to make simple graphs of change in state party ideological polarization and positioning over time using the Shor and McCarty codebook.

As illustrated above, the voting records of state legislators like Brown can also be used to assess their ideological track record and forecast their behavior as a statewide or federal elected official. While some candidates adjust their positions due to changes in the constituencies that they represent, the general pattern is that legislators tend to have relatively consistent ideological positions over time. For instance, Shor identified two likely moderates among the Republican House class of 2010 based on their voting record in state legislatures. (Nevada’s Joe Heck turned out in fact to be quite moderate compared to his party, while Illinois’s Randy Hultgren is closer to the center of the GOP caucus.)

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