Amid all the coverage of House Republicans’ unruly efforts to select a speaker who can command broad support from their fractious ranks, one name keeps coming up: the House Freedom Caucus. But what, exactly, is the House Freedom Caucus?

Pew Research Center has confirmed the identities of 36 Freedom Caucus members through representatives’ public statements, their comments to the media or their offices’ direct responses. A handful of other House members who reportedly belong to the group could not be confirmed. (The communications director for Rep. Darrell Issa of California, for example, said he could neither confirm nor deny Issa’s membership in the caucus.)

Ideologically speaking, they’re among the most conservative of House Republicans, though not all are on the rightmost end of the spectrum.

To quantify this, we used a dataset called DW-NOMINATE, first developed by political scientists Keith Poole and Howard Rosenthal in the early 1980s and refined and updated since. In simplified form, DW-NOMINATE assigns each representative a score ranging from -1 (most liberal) to +1 (most conservative) based on roll-call votes.

The 36 identified Freedom Caucus members had an average score of +0.659, more than a third higher than the average score for all other House GOP members (+0.455); the least conservative Freedom Caucus member (Steve Pearce of New Mexico) is still more conservative than the average non-Freedom Caucus House Republican.

Freedom Caucus members also have spent decidedly less time in the House. Of the 36 identified members, 26 (72%) were first elected in 2010 or later, compared with 54% of other House Republicans.

But in many other ways, the Freedom Caucus looks much like the rest of the House GOP. Of the members we were able to identify, there is only one woman (Cynthia Lummis of Wyoming) and one ethnic or racial minority (Raúl Labrador of Idaho, who is Hispanic). They’re a bit younger, with an average age of 54 (as opposed to 56 for the rest of the House Republicans), and somewhat more likely to come from the South (56% versus 45%) or the West (22% versus 16%). (Related: Freedom Caucus districts look much like other GOP-held districts)

The group, which includes many veterans of the Tea Party movement, was formed in January with the declared aim of pushing the House GOP leadership rightward on certain fiscal and social issues. More broadly, the caucus wants power shifted away from the leadership to the rank-and-file (by, for instance, giving committees more leeway on which bills to move forward and allowing more amendments to come to floor votes).

Unlike the plethora of caucuses and committees – which range from the Ad Hoc Congressional Committee for Irish Affairs to the House GOP Study Group – the Freedom Caucus does not officially disclose who belongs to it (aside from its nine founding members), though various unofficial lists have circulated. Membership is by invitation only, and meetings are not public.

Though it represents less than a sixth of House Republicans, by acting as a bloc (decisions agreed to by 80% of the caucus are supposed to be binding on all) and choosing their fights carefully, the Freedom Caucus has certainly made an impact since its formation. The group’s defiance of Speaker John Boehner, over issues such as fast-track trade authority and defunding Planned Parenthood, contributed to Boehner’s decision last month to quit the job. And the group’s decision not to back House Majority Leader Kevin McCarthy prompted McCarthy to pull out of the race and positioned the Freedom Caucus as a kingmaker.

How does such a small group get to have such a big say? Simple arithmetic: Currently, Republicans have 247 seats in the House to 188 for the Democrats, which would seem to be a comfortable majority. But if the 36 (or more) Freedom Caucus members vote as a bloc against the GOP leadership’s wishes, their effective strength falls to 211 or fewer – that is, less than the majority needed to elect a new speaker, pass bills and conduct most other business.

What most distinguishes the Freedom Caucus from other House Republicans has been their willingness to defy the wishes of leadership, up to and including Boehner, and to band together with like-minded Republicans who threaten to block any temporary measure to fund the government that didn’t also defund Planned Parenthood. That latter stance, in fact, cost the Freedom Caucus one member, Tom McClintock of California; another member, Reid Ribble of Wisconsin, quit the group earlier this month.

Related: House Freedom Caucus districts look much like other GOP-held districts

House Freedom Caucus Members

All members are Republicans

Member District House terms served Ideological score Amash, Justin MI-3 3 0.712 Blum, Rod IA-1 1 0.532 Brat, David VA-7 2 0.753 Bridenstine, Jim OK-1 2 0.752 Brooks, Mo AL-5 3 0.587 Buck, Ken CO-4 1 0.693 Clawson, Curt FL-19 2 0.669 Desantis, Ron FL-6 2 0.676 DesJarlais, Scott TN-4 3 0.568 Duncan, Jeff SC-3 3 0.767 Fleming, John LA-4 4 0.573 Franks, Trent AZ-8 7 0.751 Garrett, Scott NJ-5 7 0.690 Gosar, Paul AZ-4 3 0.573 Griffith, Morgan VA-9 3 0.514 Harris, Andy MD-1 3 0.578 Hice, Jody GA-10 1 0.700 Huelskamp, Tim KS-1 3 0.756 Jordan, Jim (chairman) OH-4 5 0.692 Labrador, Raúl ID-1 3 0.734 Loudermilk, Barry GA-11 1 0.729 Lummis, Cynthia WY-At large 4 0.670 Meadows, Mark NC-11 2 0.625 Mooney, Alex WV-2 1 0.573 Mulvaney, Mick SC-5 3 0.764 Palmer, Gary AL-6 1 0.727 Pearce, Stevan NM-2 6 0.467 Perry, Scott PA-4 2 0.623 Posey, Bill FL-8 4 0.490 Rothfus, Keith PA-12 2 0.474 Salmon, Matthew AZ-5 5 0.698 Sanford, Mark SC-1 5 0.704 Schweikert, David AZ-6 3 0.653 Stutzman, Marlin IN-3 4 0.744 Weber, Randy TX-14 2 0.797 Yoho, Ted FL-3 2 0.720 MEDIAN 3 0.691

Note: Partial terms are counted as full terms. Source: Pew Research Center reporting (confirmed Freedom Caucus members as of Oct. 19, 2015); Voteview.com Weekly Constant Space DW-NOMINATE scores by Jeff Lewis, Nolan McCarty, Keith Poole and Howard Rosenthal, updated Oct. 11, 2015; Pew Research Center analysis of the Congressional Biographical Directory (House terms served)