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154 lines
5.6 KiB
154 lines
5.6 KiB
# Voting Margin Analysis
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**Goal:** Replace binary pass/fail with continuous voting margin as the primary
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success metric for right-wing motions in the Tweede Kamer.
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**Analysis period:** 2016–2026
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**Total right-wing motions with vote data:** 2986
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**Motions passed:** 1359 (45.5%)
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**Motions failed:** 1627 (54.5%)
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---
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## 1. Methodology
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The voting margin is computed from `motions.voting_results`, which stores
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per-party vote directions as a JSON object:
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`{"PVV": "voor", "VVD": "tegen", "D66": "afwezig", ...}`.
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```
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margin = (voor - tegen) / (voor + tegen + afwezig)
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```
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Each party contributes one vote (its majority position). The margin ranges
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from -1 (unanimous rejection) to +1 (unanimous support). A margin of 0
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indicates an exact tie or no participating parties.
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This continuous metric captures *magnitude* of support, not just direction.
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A motion that passes 14-1 has margin = +0.87, while one that passes 8-7 has
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margin = +0.07. Both are "passed" in binary terms, but the former has far
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stronger parliamentary consensus.
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> **Note:** The per-party aggregation treats all parties equally, regardless of
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> seat count. This is appropriate for measuring *breadth of support across the
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> political spectrum*, which is exactly what the Overton window concept
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> concerns. Seat-weighted margins would be confounded by coalition size effects.
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---
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## 2. Correlation: Margin vs Centrist Support
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| Metric | Value |
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|--------|-------|
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| Spearman ρ | 0.812 |
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| Spearman p-value | 0.0e+00 |
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| Pearson r | 0.822 |
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| Pearson p-value | 0.0e+00 |
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The Spearman correlation is significant (ρ = 0.812, p = 0.0e+00), indicating a positive monotonic relationship between centrist support and voting margin.
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---
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## 3. Margin Distribution by Centrist Support Quartile
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### Summary Table
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| Stratum | Q1 [0.00–0.25] | Q2 (0.25–0.50] | Q3 (0.50–0.75] | Q4 (0.75–1.00] |
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|---------|:------:|:------:|:------:|:------:|
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| all | -0.263 (n=1589) | +0.087 (n=536) | +0.212 (n=230) | +0.483 (n=631) |
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| pre-2024 | -0.261 (n=1247) | +0.122 (n=357) | +0.232 (n=10) | +0.420 (n=297) |
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| post-2024 | -0.269 (n=342) | +0.017 (n=179) | +0.211 (n=220) | +0.539 (n=334) |
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### Detailed Statistics (All Motions)
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| Quartile | N | Mean | Median | Std | P25 | P75 | Min | Max |
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|----------|---|------|--------|-----|-----|-----|-----|-----|
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| Q1 | 1589 | -0.263 | -0.294 | 0.228 | -0.450 | -0.100 | -0.733 | +0.438 |
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| Q2 | 536 | +0.087 | +0.067 | 0.220 | -0.067 | +0.238 | -0.467 | +0.625 |
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| Q3 | 230 | +0.212 | +0.200 | 0.165 | +0.067 | +0.333 | -0.200 | +0.600 |
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| Q4 | 631 | +0.483 | +0.467 | 0.173 | +0.368 | +0.600 | -0.125 | +0.765 |
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**Q4 – Q1 gap in mean margin:** +0.746
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The gap of +0.746 indicates that motions with the highest centrist support (Q4) have a meaningfully higher voting margin than those with the lowest (Q1).
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---
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## 4. Pass Rate vs Margin Comparison
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This section compares the binary pass-rate metric with the continuous margin
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metric to determine whether margin captures additional information.
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| Quartile | N | Pass Rate | Mean Margin |
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|----------|---|-----------|-------------|
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| Q1 | 1589 | 12.7% | -0.263 |
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| Q2 | 536 | 59.3% | +0.087 |
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| Q3 | 230 | 92.6% | +0.212 |
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| Q4 | 631 | 99.2% | +0.483 |
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**Pass rate gap (Q4 – Q1):** +86.5%
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**Margin gap (Q4 – Q1):** +0.746
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Both pass rate and margin show a positive relationship with centrist support. Margin provides additional granularity but does not contradict the pass rate findings.
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---
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## 5. Period Stratification
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| Metric | Pre-2024 | Post-2024 | Δ |
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|--------|----------|-----------|-----|
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| N | 1911 | 1075 | |
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| Mean margin | -0.081 | +0.128 | +0.209 |
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| Mann-Whitney U | | | U=702132, p=6.6e-47 |
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| Cohen's d | | | +0.582 |
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---
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## 6. Yearly Breakdown
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| Year | N | Mean Margin | Mean CS (strict) | % Passed |
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|------|---|-------------|-----------------|---------|
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| 2016 | 6 | +0.397 | 0.667 | 100.0% |
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| 2018 | 5 | +0.538 | 1.000 | 100.0% |
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| 2019 | 195 | -0.057 | 0.380 | 42.6% |
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| 2020 | 469 | -0.074 | 0.300 | 40.5% |
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| 2021 | 425 | -0.106 | 0.175 | 34.4% |
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| 2022 | 446 | -0.093 | 0.201 | 32.5% |
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| 2023 | 365 | -0.077 | 0.255 | 34.2% |
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| 2024 | 469 | +0.175 | 0.595 | 69.5% |
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| 2025 | 455 | +0.089 | 0.474 | 57.4% |
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| 2026 | 151 | +0.099 | 0.334 | 47.7% |
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---
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## 7. Interpretation
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**Finding:** Higher centrist support is associated with higher voting margins (ρ = 0.812, p = 0.0e+00). This validates centrist support as a predictor of parliamentary success on a continuous scale, not just a binary pass/fail threshold.
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**Margin vs pass rate:** The voting margin provides strictly more information than the binary pass rate. Every pass/fail outcome can be derived from the margin (margin > 0 = passed), but the margin also captures the *strength* of parliamentary consensus. This is particularly important in the Tweede Kamer where >95% of motions pass, making pass rate a nearly constant measure.
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---
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## 8. Limitations
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- **Per-party aggregation:** All parties are weighted equally regardless of
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seat count. A motion passing with VVD (24 seats) + PVV (37 seats) has the
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same margin as one passing with SGP (3 seats) + DENK (3 seats). This is
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appropriate for measuring *breadth of cross-spectrum support* but may not
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reflect actual parliamentary power.
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- **Voting discipline:** Party-line voting is near-universal in the Dutch
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parliament. The per-party aggregation loses little information.
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- **No within-party splits:** The voting_results data shows majority party
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positions, not individual MP votes. Intra-party dissent is invisible.
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- **Missing data:** Motions without voting_results are excluded.
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---
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*Report generated by `analysis/right_wing/voting_margin.py`* |