.. _replication-secession: VanillaSC -- lost-autonomy triggers and secessionism ==================================================== :Estimator: :doc:`../vanillasc` -- :class:`mlsynth.VanillaSC` :Source: Schulte, F., Scantamburlo, M. and Ackren, M. (2026), *"Lost autonomy triggers and the rise of secessionism,"* European Political Science Review 18:175-193, DOI 10.1017/S175577392510026X. :Replication type: Path A -- reproduce the paper's empirical finding on the authors' data, and track the authors' published synthetic-control series. :Status: verified -- mlsynth recovers the paper's finding (a large post-trigger secessionist surge in both cases) and tracks the authors' synthetic closely; the agreement with their specific package is close, not value-for-value. What the paper does ------------------- Secessionist movements often surge suddenly. Schulte, Scantamburlo and Ackren (2026) argue that a "lost-autonomy trigger" -- a dramatic event symbolising a loss of self-rule -- can set off such a surge, and test this with synthetic control. They study two cases: the 2010 Spanish Constitutional Court decision that pared back Catalonia's autonomy statute, and the 1994 economic shock (a major bank collapse and Denmark-imposed constraints) in the Faroe Islands. For each treated region they build a synthetic control from the other European autonomous regions and read the post-trigger gap in secessionist sentiment (``av_sec1_all``), with an in-space placebo (RMSPE-ratio) test for inference. Their replication uses the ``SyntheticControlMethods`` Python package (``Synth``, ``pen="auto"``, ``n_optim=100``) with covariate predictors -- a penalized (Abadie-L'Hour) synthetic control with a V-optimized predictor match. Method mapping -------------- mlsynth's canonical counterpart is :class:`~mlsynth.VanillaSC` with ``backend="outcome-only"`` -- the well-posed convex problem, donor weights on the simplex minimising the pre-treatment outcome fit -- and ``inference="placebo"``, the same in-space RMSPE-ratio test. The panel is the authors' ``basedata/secession_autonomy.csv`` (13 autonomous regions, 1975-2021); each treated region is compared with the other twelve as donors, and treatment turns on at the trigger year (Catalonia 2010, Faroe Islands 1994). The finding reproduces ---------------------- Both methods deliver the paper's headline -- a large post-trigger surge in secessionist sentiment in both regions: .. list-table:: :header-rows: 1 :widths: 40 20 20 20 * - Quantity - VanillaSC (outcome-only) - Authors (SyntheticControlMethods) - correlation * - Catalonia -- post-2010 gap (ATT) - :math:`+28.0` - :math:`+23.9` - 0.92 * - Faroe Islands -- post-1994 gap (ATT) - :math:`+23.9` - :math:`+26.8` - 0.75 * - Catalonia -- pre-2010 fit RMSE - 2.66 - 2.85 - * - Faroe Islands -- pre-1994 fit RMSE - 4.92 - 5.05 - Under the in-space placebo, Catalonia is the extreme case (RMSPE-ratio :math:`p \approx 0.077`, the smallest attainable with thirteen regions), while the Faroe result is weaker -- consistent with the paper treating Catalonia as the cleaner test. The Catalonia synthetic leans on South Tyrol. A note on tightness ------------------- This is a *close* reproduction, not a value-for-value one. The reference is a different implementation -- ``SyntheticControlMethods`` optimises predictor (V) weights, auto-selects an Abadie-L'Hour penalty, and uses one hundred random restarts -- so mlsynth's deterministic outcome-only fit tracks the authors' synthetic (correlation 0.75-0.92) and lands within about fifteen percent on the ATT, rather than matching digit for digit. mlsynth's pre-treatment fit is in fact a touch tighter in both cases, which is expected: outcome-only minimises exactly the pre-period outcome error, whereas the authors' penalized, covariate-matched fit trades a little of that for predictor balance and regularisation. When mlsynth is put on the same regularised footing (``backend="penalized"`` or ``"mscmt"`` with the paper's covariates) it lands right around the authors' fit. Because the cross-package agreement is approximate, this case appears on the :doc:`../validation` dashboard as a ``documented`` row -- an honest cross-package comparison (same finding, different SC engine, about fifteen percent apart on the ATT) rather than a value-for-value ``exact`` or ``tight`` match. Verification ------------ The check is committed as the ``secession_scm`` benchmark case (`benchmarks/cases/secession_scm.py `__), which runs :class:`~mlsynth.VanillaSC` on the shipped panel and asserts the deterministic ATT, pre-treatment RMSE, in-space placebo p-value, and the correlation with the authors' published synthetic (captured under ``benchmarks/reference/secession_scm/``). The fast offline unit test is ``mlsynth/tests/test_secession_replication.py``.