Partisanship analyses of state legislative votes on legislatively referred ballot measures
This page compiles annual analyses of state legislative votes on legislatively referred ballot measures. Each report shows how Democratic and Republican lawmakers voted on each measure, the level of support from legislators of each party, the difference between them, and how electors voted on the measures.
Unlike citizen-initiated ballot measures, legislatively referred ballot measures appear on the ballot due to a vote of the state legislature. This allows for an analysis of how members of the two major political parties—Democrats and Republicans—voted on each measure.
Ballotpedia uses a Partisan Direction Index (PDI) to illustrate the level of partisan support behind each referral. The PDI measures the difference between the percentages of Democratic and Republican legislators who voted in favor of a measure. Scores range from –100% to +100%, where
- –100% indicates support only from Democrats,
- +100% indicates support only from Republicans, and
- 0% indicates equal support from both parties.
Each ballot measure receives both a numerical PDI score and a partisan classification—Democratic, Lean Democratic, Bipartisan, Lean Republican, or Republican—reflecting the partisan breakdown of the legislative vote that placed the measure on the ballot.
The PDI allows for quickly identifying which party supported a measure and tracking long-term trends, such as which policy areas typically receive partisan or bipartisan support, as well as approval rates for different partisan classes.
Years
Click on a year to view that year’s partisanship analysis of state legislative votes on legislatively referred ballot measures.
- 2026
- 2025
Partisan Direction Index (PDI)
The Partisan Direction Index (PDI) measures the partisan support behind a legislative referral, a type of ballot measure that appears on the ballot due to the vote of a state legislature. Referrals can be constitutional amendments or statutes. The index ranges from -100%to +100%, where –100% means only Democrats voted 'Yes,' +100% means only Republicans did, and zero means equal support from both parties. PDI accounts for the percentage of each party's members who voted 'Yes.'
The classification includes both:
- a continuous number between –100% and +100% rounded to one decimal place, and
- a corresponding category, such as Lean Republican or Bipartisan.
For example, in 2024, the Iowa State Legislature referred Amendment 1 to the ballot. Among legislators, 65.4% of Democrats and 100.0% of Republicans voted 'Yes.' Using the PDI formula, this results in a score of +34.6%, which is classified as Lean Republican.
The table below shows how percentage ranges translate into PDI classifications. The classifications are based on dividing the full –100% to +100% scale into five equal parts.
| PDI Range (Continuous) | Class (Ordinal) | Description |
|---|---|---|
| -100% to -60% | Democratic | Mostly or entirely Democratic support; little or no Republican support |
| -60% to -20% | Lean Democratic | Predominantly Democratic, with some Republican support |
| -20% to +20% | Bipartisan | Both parties showed majority support. No single party drove the support |
| +20% to +60% | Lean Republican | Predominantly Republican, with some Democratic support |
| +60% to +100% | Republican | Mostly or entirely Republican support; little or no Democratic support |
See also
Footnotes
