How the index is built.

The four measured parts

Each part is turned into a score from 0 to 100, where 100 is the most independent. The index is the weighted average of the four parts: lobby money 22 percent, PAC share 22 percent, trading 16 percent and crossing the aisle 40 percent. When a part is missing for a member, it takes the median of every member who has it, so a gap neither raises nor lowers a score, and the member is marked partial. The medians today are lobby money 49.5, PAC share 54.7, trading 100.0 and crossing the aisle 49.5. A member is scored only when FEC campaign money is on file.

1. Pro-Israel lobby money. TrackAIPAC's Israel Lobby Total, the career sum of money from pro-Israel PACs and their large donors plus their outside spending for the member, built from FEC records. The score falls on a log scale: $0 scores 100, $10,000 about 74, $100,000 about 50, $1 million about 25 and $10 million or more 0. Members TrackAIPAC marks as rejecting AIPAC, with no dollar figure shown, are counted as zero.
2. PAC money share. The money a member's campaign took from PACs and other non-party committees, as a share of everything it raised this cycle, from the FEC's candidate summary. The score falls in a straight line from 100 at no PAC money to 0 at a 70 percent share. Members who raised under $25,000 are left out of this part.
3. Stock trading. The trades a member reported in the last year and their estimated dollar volume, from Quiver Quantitative. The count and the volume each get a log scale score and the two are averaged: one trade scores about 93 on the count, ten about 77, a hundred about 56 and a thousand about 34; $100,000 in volume scores about 60 and $10 million about 20.
4. Crossing the aisle. Eight scorecards, four that lean left, League of Conservation Voters, ProgressivePunch, AFL-CIO, Human Rights Campaign, and four that lean right, Heritage Action, CPAC ratings, Club for Growth, America First Foundation. Each card is rescaled so the average member of the party it backs sits at 100 and the average member of the party it opposes at 0. The left cards are averaged, the right cards are averaged, every card counting the same, and the part is the mean of the two sides, held between 0 and 100. By construction the average Democrat and the average Republican both land at 50 here, so this part cannot favor either party. A member scores higher by earning credit from the other side's groups and lower by falling short of their own side's. A side needs at least two cards on file; otherwise it takes the median of the member's own party.

Grades

Grades are fixed cutoffs on the index, not a curve, so every member could in principle earn an A.

Not scored yet: votes that helped donors

The fourth part we want is a test of whether a member's votes line up with the industries that fund them. That needs each donor's industry, which the public FEC pages do not give and which we cannot yet read from an industry coded source. Rather than guess, the index leaves this part out and every member page says so. It will be added once the data can be read in full.

Why the scorecards are rescaled

Left leaning groups give the typical Democrat a score near 96 and the typical Republican near 2; right leaning groups spread their scores more, and the America First Foundation gives Democrats about 34. Averaging the raw scores would hand one party a head start. Rescaling each card between the two party averages first removes that, so the blend measures how a member compares with their own party and the other, not which party they belong to. Moderates are not automatically rewarded: groups on both sides often score them below their own party, and the part shows that.