# Overton Window Breakpoint Analysis

**Goal:** Quantify the 2024 structural break in centrist support
and content extremity for right-wing motions in the Tweede Kamer.

**Analysis period:** 2016–2026
**Right-wing parties:** PVV, FVD, JA21, SGP
**Centrist parties:** VVD, D66, CDA, NSC, BBB, CU
**Left parties:** PvdA, GL, SP, PvdD, Volt, DENK, Bij1

---

## 1. Yearly Aggregate Metrics (All Right-Wing Motions)

| Year | N (RW) | Centrist Support (Strict) | Extremity | Right Support | Left Opp. |
|------|--------|---------------------------|-----------|---------------|----------|
| 2016 | 6 | 0.667 | 2.00 | 1.000 | 0.708 |
| 2017 | 0 | N/A | N/A | N/A | N/A |
| 2018 | 5 | 1.000 | 1.40 | 0.800 | 0.480 |
| 2019 | 195 | 0.380 | 2.14 | 0.838 | 0.746 |
| 2020 | 469 | 0.300 | 2.26 | 0.818 | 0.758 |
| 2021 | 425 | 0.175 | 2.24 | 0.903 | 0.788 |
| 2022 | 446 | 0.201 | 2.16 | 0.891 | 0.820 |
| 2023 | 365 | 0.255 | 2.24 | 0.900 | 0.821 |
| 2024 | 469 | 0.595 | 1.99 | 0.885 | 0.756 |
| 2025 | 455 | 0.474 | 2.25 | 0.895 | 0.799 |
| 2026 | 151 | 0.334 | 2.33 | 0.916 | 0.834 |


## 2. Pre/Post 2024 Comparison

**Break year:** 2024

### All right-wing motions

| Metric | Pre-2024 Mean | Post-2024 Mean | Δ | Cohen's d |
|--------|--------------|---------------|-----|-----------|
| Centrist Support | 0.251 | 0.507 | +0.256 | +0.65 |
| Extremity | 2.21 | 2.15 | -0.07 | -0.09 |

**Interpretation:** Cohen's d values quantify effect sizes (|d| < 0.2 small, 0.5 medium, > 0.8 large).
These are descriptive, not inferential — with only 8 pre-2024 years and 3 post-2024 years, statistical significance is not claimed.

### Opposition-only right-wing motions

| Metric | Pre-2024 Mean | Post-2024 Mean | Δ | Cohen's d | N pre / N post |
|--------|--------------|---------------|-----|-----------|---------------|
| Centrist Support | 0.130 | 0.423 | +0.293 | +0.85 | 1295 / 437 |
| Extremity | 2.28 | 2.17 | -0.10 | -0.14 | 1295 / 437 |

**Interpretation gate:** If opposition metrics also rise post-2024, the shift is not
purely coalition-driven. If opposition metrics stay flat while overall metrics rise,
the shift is coalition-specific.

## 3. Coalition Composition

2016-2017: Rutte II (VVD/PvdA). 2018-2021: Rutte III (VVD/CDA/D66/CU). 2022-2023: Rutte IV (VVD/D66/CDA/CU). 2024 split: Rutte IV (VVD/D66/CDA/CU) for Jan-Jun 2024, Schoof (PVV/VVD/NSC/BBB) for Jul-Dec 2024. 2025-2026: Schoof (PVV/VVD/NSC/BBB). Period detection uses motion date, not just year.

Submitter party is parsed from motion title prefixes
(e.g., "Motie van het lid Wilders over ..."). Only the lead submitter's party is
considered. Multi-submitter motions may have a coalition member as co-submitter
but still be counted as opposition if the lead submitter is not in the coalition.

## 4. Domain Decomposition

Migration = category `asiel/vreemdelingen`. Non-migration = all other categories.

| Domain | Pre-2024 Mean CS | Post-2024 Mean CS | Δ CS |
|--------|-----------------|------------------|------|
| Migration | 0.146 | 0.361 | +0.215 |
| Non-migration | 0.435 | 0.487 | +0.052 |

## 5. Extremity-Stratified Centrist Support

| Bucket | Period | N | Mean CS | Median CS | P25 | P75 |
|--------|--------|---|---------|-----------|---|-----|
| 1-2 (mild) | Pre-2024 | 221 | 0.422 | 0.500 | 0.000 | 1.000 |
| | Post-2024 | 181 | 0.728 | 1.000 | 0.667 | 1.000 |
| 2-3 (moderate) | Pre-2024 | 1205 | 0.267 | 0.000 | 0.000 | 0.500 |
| | Post-2024 | 640 | 0.497 | 0.500 | 0.000 | 1.000 |
| 3-4 (high) | Pre-2024 | 352 | 0.150 | 0.000 | 0.000 | 0.000 |
| | Post-2024 | 175 | 0.419 | 0.333 | 0.000 | 0.667 |
| 4-5 (extreme) | Pre-2024 | 133 | 0.091 | 0.000 | 0.000 | 0.000 |
| | Post-2024 | 79 | 0.275 | 0.000 | 0.000 | 0.667 |


**Key test:** If centrist support for high-extremity motions (3-5) rose
disproportionately post-2024 while centrist support for mild motions stayed flat,
centrists are more tolerant of extreme content — direct Overton shift evidence.
If centrist support rose uniformly across all buckets, the shift is about volume
(more motions) rather than tolerance. If only the 1-2 bucket rose, right-wing
parties filed milder motions post-2024 and the 'shift' is illusory.

## 6. Left-wing support for right-wing motions

| Year | N | Mean left_support_mp |
|------|---|---------------------|
| 2016 | 6 | 0.2917 |
| 2018 | 5 | 0.5200 |
| 2019 | 195 | 0.2531 |
| 2020 | 469 | 0.2414 |
| 2021 | 425 | 0.2113 |
| 2022 | 446 | 0.1807 |
| 2023 | 365 | 0.1779 |
| 2024 | 469 | 0.2441 |
| 2025 | 455 | 0.2015 |
| 2026 | 151 | 0.1594 |


| Metric | Pre-2024 Mean | Post-2024 Mean | Δ |
|--------|--------------|---------------|-----|
| Left Support (MP) | 0.2680 | 0.2017 | -0.0663 |

**Interpretation:** Left parties moved from 26.8% to 20.2% support — a 0.1 point shift. Whether this represents leftward Overton expansion depends on whether left parties are tolerating or actively supporting right-wing positions.

![Figure 3: Left-wing party support for right-wing motions](breakpoint_figure_3.png)

## 7. Manual Extremity Audit

**Audit notes:** Perform manual audit by reviewing the motions below. Record agreement per motion. Note whether the LLM score appears driven by *stylistic extremity* (inflammatory phrasing) or *material impact* (substantive rights restriction, institutional change). If agreement < 70%, flag LLM scoring as unreliable for the stratified analysis.

| # | Year | Category | LLM Score | Bucket | Agreed? | Driver |
|---|------|----------|-----------|--------|---------|--------|
| 1 | 2024 | economie/belasting | 1 | 1-2 (mild) | | |
| 2 | 2020 | economie/belasting | 1 | 1-2 (mild) | | |
| 3 | 2019 | veiligheid/justitie | 1 | 1-2 (mild) | | |
| 4 | 2025 | economie/belasting | 1 | 1-2 (mild) | | |
| 5 | 2022 | sociaal/jeugd | 1 | 1-2 (mild) | | |
| 6 | 2021 | corona/pandemie | 2 | 2-3 (moderate) | | |
| 7 | 2021 | zorg/gezondheid | 2 | 2-3 (moderate) | | |
| 8 | 2020 | economie/belasting | 2 | 2-3 (moderate) | | |
| 9 | 2025 | veiligheid/justitie | 2 | 2-3 (moderate) | | |
| 10 | 2020 | economie/belasting | 2 | 2-3 (moderate) | | |
| 11 | 2020 | veiligheid/justitie | 3 | 3-4 (high) | | |
| 12 | 2025 | klimaat/milieu | 3 | 3-4 (high) | | |
| 13 | 2019 | asiel/vreemdelingen | 3 | 3-4 (high) | | |
| 14 | 2019 | landbouw/stikstof | 3 | 3-4 (high) | | |
| 15 | 2020 | klimaat/milieu | 3 | 3-4 (high) | | |
| 16 | 2020 | veiligheid/justitie | 4 | 4-5 (extreme) | | |
| 17 | 2021 | defensie/buitenland | 4 | 4-5 (extreme) | | |
| 18 | 2023 | asiel/vreemdelingen | 4 | 4-5 (extreme) | | |
| 19 | 2025 | asiel/vreemdelingen | 4 | 4-5 (extreme) | | |
| 20 | 2019 | sociaal/jeugd | 4 | 4-5 (extreme) | | |


## 8. Limitations

- **Small-N time series:** 8 pre-2024 years and at most 3 post-2024 years (2026 is partial).
   Effect sizes are descriptive, not confirmatory.
- **LLM extremity scores:** Content-based, not independently validated beyond the
   manual audit above. See §7 for agreement rate and noted biases.
- **Coalition composition:** Hardcoded per year. 2024 is ambiguous (Rutte IV until July,
   Schoof thereafter). Early 2024 motions may be miscoded as Schoof-era.
- **Submitter party identification:** Parsed from motion title prefixes (e.g.,
   'Motie van het lid X'). May be inaccurate for multi-submitter motions or
   complex title formats.
- **Keyword penetration not analyzed:** The right-wing keyword set was derived
   differentially from right-wing motions, making it circular for adoption analysis.

## 9. Figures

![Figure 1: Centrist Support Over Time](breakpoint_figure_1.png)
![Figure 2: Extremity Trends and Stratified Centrist Support](breakpoint_figure_2.png)
![Figure 3: Left-wing party support for right-wing motions](breakpoint_figure_3.png)

## 10. Conclusion

*(Fill in after reviewing all indicators and audit results.)*