How the Democratic–Republican scale is worked out

Every position on this site comes from roll-call votes that members of Congress personally cast. Each one is placed between the side most Democrats took and the side most Republicans took on the same votes. This page is the whole method and the whole list, because a position you cannot check is just an opinion with a number attached.

The method, in six steps

Pick the values. 12 of them, each one a thing a person might actually be voting on. Both ends of every scale are written as a position someone holds — “cutting emissions faster” against “cheaper energy now and fewer federal mandates” — never as a virtue and its absence.
Pick the votes. 130 roll calls in total, chosen by hand from the 117th, 118th and 119th Congresses. Near-unanimous votes are excluded: a bill that passed 420–2 separates nobody.
Write down what each side of each vote did. This is the judgment, and it is recorded in a sentence next to every vote. It has to be, because the subject of a vote does not tell you its direction — see below.
Count where each party stood. On every vote, the Democratic side is whichever way most Democrats voted, and the Republican side whichever way most Republicans voted, counted from the roll call itself with each member's party on the day. 126 of the 130 votes split the parties that way. On the rest, most of both parties voted the same way; those are still listed, but they cannot say which side anyone was on, so they do not move anyone on the scale.
Place each member on each value. A member's position is the share of the value's party-split votes they cast on the Republican side: 0 means the Democratic side every time, 100 the Republican side every time, 50 an even split. Only votes they cast count; absences are shown beside the position and never counted for either side. A position from fewer than 4 votes is still drawn, with a hollow marker and its count beside it, because it is not yet a pattern.
Roll the values up. The overall position is the average of the member's value positions, with each value counted once however many votes stand behind it — so the values with the most votes do not drown out the rest. For the same reason a value with fewer than 4 of their votes is left out of it: at equal weight, three votes would move the overall figure as much as twelve. It needs at least 3 values with 4 or more; the average of one or two is not an overall anything.

Why the direction of a vote is never guessed

The obvious shortcut is to find the votes about a subject and assume a “yes” supports it. That shortcut is wrong often enough to be dangerous, and the current Congress is where it fails hardest. Two real resolutions, same agency, same subject, opposite meaning:

S.J.Res. 18 strikes the Consumer Financial Protection Bureau's cap on overdraft fees. A yes removes a consumer protection.
S.J.Res. 130 strikes the same Bureau's withdrawal of its overdraft opt-in guidance. A yes restores a consumer protection.

Any classifier keying on “Consumer Financial Protection Bureau” reads the second one backwards. So what each side of every vote did was read and written down by a person, and where each party stood is counted from the votes rather than assumed from the subject. You can read both beside every vote.

What this does not measure

Challengers. Someone who has never served in Congress has no roll-call record, so they have no position on this scale. That is the honest answer, not a gap waiting to be filled, and nothing here is inferred from a party label, endorsements or who funds them. A race page shows what each campaign has raised instead, in its own block below the record: money is a fact about a campaign, not a vote anyone cast, and it is never placed on this scale.
Ideology in general. The scale measures which party's side a member took on these particular votes, not how liberal or conservative they are. A member can land toward the middle for opposite reasons: by breaking with their party toward the other one, or by voting against their own party's bill because it did not go far enough. A roll call records both the same way.
Why someone voted. A roll call records a position, not a reason. Members vote against bills they agree with over a single provision, to preserve a procedural right, or because of a deal the record does not show. A party leader who switches to “nay” so they can move to reconsider a failed vote is counted on the side they voted.
Where the parties will stand next. Each side is where a party stood on the day. On some values that moves with who holds the White House — war powers votes split the parties one way under one president and can split them the other way under the next.
Both chambers equally. House members cannot be placed on health care and prescription costs and taxes and who pays them at all: none of their party-split votes were House votes. On reproductive health care, workers, wages and care and voting and elections, fewer than 4 were, so a representative's position there is drawn thin and left out of their overall position. A representative's overall position is averaged from the other 7 at most. A senator's position on guns and war powers is drawn thin for the same reason. The two chambers vote on different bills, so a representative and a senator at the same position were measured on different votes.
Anything outside these votes. Committee work, sponsorship, amendments that never reached a vote, and everything done in a state legislature or a governor's office are all invisible here.

The 12 values

Each links to every vote behind it, with how each party voted and the reasoning for what each side did. See every sitting member on the overall scale.

Climate and clean energy
14 key votes · 6 House and 7 Senate split the parties
Votes on greenhouse-gas limits, vehicle and appliance efficiency standards, and the tax credits behind wind and solar.
Democratic side: Cutting greenhouse-gas emissions fasterRepublican side: Cheaper energy now and fewer federal mandates
Clean air, water and public land
15 key votes · 9 House and 6 Senate split the parties
Votes on pollution limits, endangered species, and how much federal land is opened to drilling, mining and logging.
Democratic side: Stronger limits on pollution and developmentRepublican side: Fewer federal restrictions on land and industry
Health care and prescription costs
11 key votes · 0 House and 11 Senate split the parties
Votes on Medicaid and Medicare funding, Affordable Care Act subsidies, and what the government may do about drug prices.
Democratic side: Broader public coverage and lower drug pricesRepublican side: Less federal spending and a smaller government role
Reproductive health care
14 key votes · 3 House and 11 Senate split the parties
Votes on abortion access, contraception, fertility treatment and the federal funding attached to each.
Democratic side: Protecting access to abortion, contraception and IVFRepublican side: Restricting abortion and the funding behind it
Guns
6 key votes · 4 House and 2 Senate split the parties
Votes on background checks, the weapons that may be sold, and the records federal agencies may keep.
Democratic side: Tighter limits on firearmsRepublican side: Fewer restrictions on lawful gun owners
Immigration
12 key votes · 4 House and 8 Senate split the parties
Votes on border enforcement, detention and deportation funding, and the benefits available to people without permanent status.
Democratic side: More legal protection and processing capacityRepublican side: Stricter enforcement and less federal benefit access
Workers, wages and care
9 key votes · 3 House and 6 Senate split the parties
Votes on the minimum wage, union bargaining rights, and funding for child care and caregiving.
Democratic side: Stronger bargaining rights and higher wage floorsRepublican side: More employer flexibility and lower labour costs
Taxes and who pays them
6 key votes · 0 House and 4 Senate split the parties
Votes on top-bracket and corporate rates, targeted credits, and how much the IRS is funded to collect what is owed.
Democratic side: Higher taxes at the top and stronger collectionRepublican side: Lower rates and a smaller tax administration
Civil rights and discrimination
9 key votes · 5 House and 4 Senate split the parties
Votes on anti-discrimination law covering sex, age, pregnancy, sexual orientation and gender identity.
Democratic side: Broader federal anti-discrimination protectionRepublican side: Narrower federal rules, more left to states
Voting and elections
10 key votes · 2 House and 8 Senate split the parties
Votes on the Voting Rights Act, registration and identification requirements, and federal election standards.
Democratic side: Wider access to the ballotRepublican side: Tighter eligibility and identity checks
War powers
13 key votes · 9 House and 3 Senate split the parties
Votes on whether forces already committed abroad need explicit authorisation from Congress to stay there.
Democratic side: Requiring Congress to authorise military forceRepublican side: Leaving the deployment decision with the President
Consumer financial protection
11 key votes · 4 House and 7 Senate split the parties
Votes on overdraft and medical-debt rules, and on the funding and reach of the Consumer Financial Protection Bureau.
Democratic side: Stronger federal protection for borrowersRepublican side: Lighter regulation of banks and lenders

Disagree with a call? Every vote links to its full roll call, with the question as the chamber put it and how each member voted, so you can take the raw record and reach your own conclusion.