What it measures
Since 1789 the Constitution has let one fifth of the members present demand that “the Yeas and Nays” be entered on the Journal (Art. I, §5). PL reads that record: on contested roll calls, the share of a member’s Yea/Nay votes that matched their own caucus majority. It is a box-score line.
By the numbers
| Measure | Value | Source |
|---|---|---|
| Share of House roll calls on which the two caucus majorities voted on opposite sides, 1969 | 31.1% | Brookings, Vital Statistics on Congress, Table 8-3 (from CQ party-unity studies) |
| Same measure, House, 1964 | 54.9% | Brookings, Vital Statistics on Congress, Table 8-3 (from CQ party-unity studies) |
| Same measure, House, 2017 (highest in the 1953–2022 table) | 76.0% | Brookings, Vital Statistics on Congress, Table 8-3 (from CQ party-unity studies) |
| Same measure, House, 2022 (latest in table) | 53.1% | Brookings, Vital Statistics on Congress, Table 8-3 (from CQ party-unity studies) |
| Same measure, Senate, 2022 | 83.1% | Brookings, Vital Statistics on Congress, Table 8-3 (from CQ party-unity studies) |
| Same measure, 119th Congress (2025–26) | data needed | not yet located; not estimated |
The table measures roll calls; PL measures members. Related, not identical. Constitutional text: Art. I, §5. Full formula: Methodology.