# SVD Center Drift & Axis Stability Report

## Axis Stability Validation

**Stability threshold:** Spearman ρ ≥ 0.7 for both axes. Maximum unstable pairs allowed: 2.

**Result:** 9 unstable pair(s) out of 10 consecutive window pairs.

**CONCLUSION: SVD axes are too unstable for longitudinal comparison. Positions may reflect re-orientation rather than genuine drift. The following drift metrics and chart should be interpreted with extreme caution.**

- Mean axis-1 correlation: 0.0054
- Mean axis-2 correlation: 0.2128

### Per-Pair Stability Details

| Window Pair | Axis 1 ρ | Axis 2 ρ | Unstable | Shared Parties |
|---|---|---|---|---|
| 2016-2017 | -0.439 | 0.257 | **YES** | BBB, CDA, ChristenUnie, D66, DENK, GrBvK, GroenLinks-PvdA, Houwers, Klein, Krol, Monasch, NSC, PVV, PvdD, SGP, SP, VVD, Van Vliet |
| 2017-2018 | -0.779 | 0.876 | **YES** | 50PLUS, BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, Groep Van Haga, Krol, NSC, PVV, PvdD, SGP, SP, VVD |
| 2018-2019 | 0.897 | -0.024 | **YES** | 50PLUS, BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, Groep Van Haga, Krol, NSC, PVV, PvdD, SGP, SP, VVD |
| 2019-2020 | -0.819 | 0.353 | **YES** | 50PLUS, BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, Groep Van Haga, Krol, NSC, PVV, PvdD, SGP, SP, VVD, vKA |
| 2020-2021 | 0.797 | -0.772 | **YES** | 50PLUS, BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, Groep Van Haga, Krol, NSC, PVV, PvdD, SGP, SP, VVD, vKA |
| 2021-2022 | 0.893 | 0.910 | no | BBB, BIJ1, CDA, ChristenUnie, D66, DENK, Ephraim, FVD, Fractie Den Haan, GroenLinks-PvdA, Groep Van Haga, JA21, NSC, PVV, PvdD, SGP, SP, VVD, Volt |
| 2022-2023 | 0.889 | -0.379 | **YES** | BBB, BIJ1, CDA, ChristenUnie, D66, DENK, Ephraim, FVD, Fractie Den Haan, GroenLinks-PvdA, Groep Van Haga, JA21, NSC, PVV, PvdD, SGP, SP, VVD, Volt |
| 2023-2024 | -0.229 | 0.821 | **YES** | BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, JA21, NSC, PVV, PvdD, SGP, SP, VVD, Volt |
| 2024-2025 | -0.757 | 0.779 | **YES** | BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, JA21, NSC, PVV, PvdD, SGP, SP, VVD, Volt |
| 2025-2026 | -0.400 | -0.694 | **YES** | 50PLUS, BBB, CDA, ChristenUnie, D66, DENK, FVD, GroenLinks-PvdA, JA21, NSC, PVV, PvdD, SGP, SP, VVD, Volt |

## Centrist Center of Gravity

| Window | Centrist Ax1 | Centrist Ax2 | Right Ax1 | Right Ax2 | Centrist Parties Present | Right Parties Present |
|---|---|---|---|---|---|---|
| 2016 | 5.1514 | 0.1220 | 5.6432 | 0.5936 | BBB, CDA, ChristenUnie, D66, NSC, VVD | PVV, SGP |
| 2017 | -3.6524 | -0.7100 | -3.7095 | 1.3546 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, PVV, SGP |
| 2018 | 5.1662 | -0.8347 | 2.2336 | 3.7263 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, PVV, SGP |
| 2019 | 11.7312 | -2.6126 | 7.1092 | 6.5966 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, PVV, SGP |
| 2020 | -27.1482 | 2.8304 | -9.2387 | -14.1063 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, PVV, SGP |
| 2021 | -15.9032 | -0.6795 | -6.3142 | 19.8728 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, JA21, PVV, SGP |
| 2022 | -28.5270 | -0.6204 | -3.8504 | 19.8373 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, JA21, PVV, SGP |
| 2023 | -15.7130 | 0.1571 | -5.0623 | -15.8667 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, JA21, PVV, SGP |
| 2024 | 26.2822 | 19.2003 | 24.9072 | -0.8372 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, JA21, PVV, SGP |
| 2025 | -8.1667 | 12.0249 | -14.5604 | 1.7604 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, JA21, PVV, SGP |
| 2026 | -13.6251 | 3.4321 | -3.8011 | 16.7538 | BBB, CDA, ChristenUnie, D66, NSC, VVD | FVD, JA21, PVV, SGP |

## Drift Metrics (UNRELIABLE — Axes Unstable)

Drift metrics were computed but are unreliable due to axis instability. Cross-window comparisons on unstable axes conflate positional change with axis re-orientation.

## Chart

![SVD Drift Chart](svd_drift_chart.png)

## Interpretability Statement

SVD axes are too unstable for longitudinal comparison. The trajectory plotted above may reflect axis re-orientation (each SVD window independently determines its principal axes) rather than genuine ideological drift. We recommend against drawing conclusions from this analysis.

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*Note: SVD axes reflect voting patterns, not semantic content. A shift means voting behavior changed, not that parties changed their rhetoric. See: docs/solutions/best-practices/svd-labels-voting-patterns-not-semantics.md*