Methodology

Party Unity Score

Concord's per-Member Party Unity Score is modeled on the Congressional Quarterly Almanac's Party Unity Score methodology, published annually since 1953. It measures how often a Member votes with their party's majority — but only on the votes where the two major parties actually divided.

Party-unity vote

A roll-call vote where a majority of Republican Yea/Nay positions opposed a majority of Democratic Yea/Nay positions on that vote. Positions of "Present" and "Not Voting" are excluded from each party's majority calculation. Independents do not count toward either majority. Unanimous and near-unanimous votes — where both parties land on the same side — are not party-unity votes.

Denominator

Count of party-unity votes the Member cast a Yea or Nay on, within one Congress. Votes where the Member was Present or Not Voting are excluded.

Numerator

Of those denominator votes, the count where the Member's position agreed with their party's majority position on that vote. The Member's party is taken as their modal party across their party-unity positions in that Congress (a Member who switches party mid-Congress is scored against whichever party they spent more votes in).

Independents

Members whose modal party is Independent receive no Party Unity Score — no party majority exists for them to agree or disagree with. Their profile shows "no party-unity score (Independent)" instead of a number.

Low-N suppression

Members with fewer than 10 party-unity votes in a Congress are shown as "not enough votes yet" rather than a percentage. The 10-vote threshold is conventional and avoids the "100% with party on 3 votes" early-Congress noise.

Chamber scope

Each chamber's score is computed independently from positions cast in that chamber. Senate party-unity votes are derived from Senate positions only; House party-unity votes from House positions only. Members who served in both chambers in a single Congress (rare chamber-switchers) see two scores per Congress, one per chamber.

The full technical definition lives in ADR 0011.