IESET.
Hypotheses·distribution·tax_inequality_nz_2010_gst_rate_swap

New Zealand's 2010 tax swap (GST rate raised from 12.5 to 15 percent, paired with personal income tax rate cuts including the top rate from 38 to 33 percent) produced a measurable rise in the New Zealand top-1 pretax income share over 2010-2014 vs Anglo-comparator synthetic control, with smaller but detectable rise in the disposable-income Gini coefficient driven by the GST regressivity.

The discriminating test pairs top-1 share rise vs disposable Gini rise.

PARTIALengine/runs/tax_inequality_nz_2010_gst_rate_swap

PARTIAL — mean_gap=+4.113, |gap|/pre_sd=1.1, p_perm=0.333 (gap below 0.5×pre_sd or placebo p≥0.10)

confidence cueThe result is useful, but not decisive. Treat it as a clue, not a settled conclusion.

policy briefMixed or noisy

In ordinary language

Over a long period, do more market-oriented institutions translate into higher income or productivity, once the comparison looks beyond a single success story?

plain answer

The evidence is suggestive but not decisive. mean_gap=+4.113, |gap|/pre_sd=1.1, p_perm=0.333 (gap below 0.5×pre_sd or placebo p≥0.10)

why it matters

Distributional claims often sound morally clear but are empirically complex. This test asks whether the proposed channel explains real differences across places.

how the test works

It compares 6 country or place units from 2000 to 2018, using a synthetic control design, with fixed effects for country and year.

what was measured
What changed
  • Nz 2010 gst swap post
  • Top marginal income tax rate
What we checked
  • Top 1pct pretax income share
  • Inequality disposable income
what this does not prove

A single test is not the whole truth. It narrows the claim under a specific sample, time period, and method. Strong policy conclusions need the pattern to survive nearby tests, alternative data, and serious objections.

verification

No evidence packet has been generated yet.

Results

engine/runs/tax_inequality_nz_2010_gst_rate_swap
1007550250200020092018NZLAUSCANGBRIRLUSA
illustrative sketch · run pending
No coefficients yet. When the model fires, this chart will show top_1pct_pretax_income_share across 6 sampled countries over 2000–2018.
The shapes above are stylised — none of the lines are real data.
Placeholder for tax_inequality_nz_2010_gst_rate_swap. Published chart will be generated from engine/runs/tax_inequality_nz_2010_gst_rate_swap/chart_data.json.

Pre-registration

registration ordering unverified
first-spec commit 4c8ce8e · 2026-07-18T22:11:21Z
run generated · 2026-04-30T12:29:43Z
Run timestamp predates this path's first git-add commit (rebase, rename, or pre-git local run). Spec hash is still the path's first-add commit — not repository HEAD — but ordering is not a clean pre-registration proof.

New Zealand's 2010 tax swap (GST rate raised from 12.5 to 15 percent, paired with personal income tax rate cuts including the top rate from 38 to 33 percent) produced a measurable rise in the New Zealand top-1 pretax income share over 2010-2014 vs Anglo-comparator synthetic control, with smaller but detectable rise in the disposable-income Gini coefficient driven by the GST regressivity. The discriminating test pairs top-1 share rise vs disposable Gini rise.

Falsification criterion — what would disprove this

set before the run · honoured after

This hypothesis is considered falsified if:

SUPPORTED if NZ top-1 share rises by at least 0.75 percentage points over 2010-2014 vs Anglo synthetic control AND disposable-income Gini rises by at least 0.5 Gini-points at p<0.10. REFUTED if no detectable movement on either margin at the four-year horizon.

formal test & threshold
test:      Synthetic-control with Anglo donor pool (AUS, CAN, GBR, IRL, USA), treated NZL 2010.

Method

Template
synthetic_control
Fixed effects
country, year
Clustering
country
Sample
6 countries · 2000 – 2018
Evidence type
associational

Synthetic-control with Anglo donor pool. Treated NZL 2010. Placebo- in-time 2005.

Data

VariableSourceTransform
top_1pct_pretax_income_share
outcome
owid:top-1-share-of-total-incometier 2
level
gini_disposable_income
outcome
world_bank_wdi:SI.POV.GINItier 2
level
nz_2010_gst_swap_post
treatment
constructed:indicator = 1 for NZL, year >= 2010tier 5
indicator
top_marginal_income_tax_rate
treatment
owid:top-marginal-income-tax-ratetier 2
level
log_real_gdp_per_capita
control
world_bank_wdi:NY.GDP.PCAP.KDtier 2
log
trade_openness
control
world_bank_wdi:NE.TRD.GNFS.ZStier 2
level

● ready  · ● pending  · ● reconstruct-needed

Detailed result card

Result card — tax_inequality_nz_2010_gst_rate_swap

Verdict: PARTIAL — mean_gap=+4.113, |gap|/pre_sd=1.1, p_perm=0.333 (gap below 0.5×pre_sd or placebo p≥0.10)

Pre-registration

  • Claim: New Zealand's 2010 tax swap (GST rate raised from 12.5 to 15 percent, paired with personal income tax rate cuts including the top rate from 38 to 33 percent) produced a measurable rise in the New Zealand top-1 pretax income share over 2010-2014 vs Anglo-comparator synthetic control, with smaller but detectable rise in the disposable-income Gini coefficient driven by the GST regressivity. The discriminating test pairs top-1 share rise vs disposable Gini rise.
  • Falsification rule: SUPPORTED if NZ top-1 share rises by at least 0.75 percentage points over 2010-2014 vs Anglo synthetic control AND disposable-income Gini rises by at least 0.5 Gini-points at p<0.10. REFUTED if no detectable movement on either margin at the four-year horizon.

Synthetic-control estimate

  • shape: synth_did
  • treated_country: NZL
  • event_year: 2010
  • n_donors: 5
  • donor_weights (top): {'AUS': 1.0, 'CAN': 0.0, 'GBR': 0.0, 'IRL': 0.0, 'USA': 0.0}
  • pre_rmse: 5.432529797433236
  • pre_period_sd: 3.6849376596566126
  • mean_post_gap: 4.112857142857143
  • end_period_gap: 1.0199999999999996
  • post_period_years: [2010, 2018]
  • placebo_p_value: 0.3333333333333333
  • n_placebos: 5
  • method: synthetic-control via NNLS, permutation inference

Variables resolved

  • owid:top-1-share-of-total-income → top_1pct_pretax_income_share (outcome, n=3294)
  • world_bank_wdi:SI.POV.GINI → gini_disposable_income (outcome, n=2430)
  • owid:top-marginal-income-tax-rate → top_marginal_income_tax_rate (treatment, n=590)
  • world_bank_wdi:NY.GDP.PCAP.KD → log_real_gdp_per_capita (controls, n=14066)
  • world_bank_wdi:NE.TRD.GNFS.ZS → trade_openness (controls, n=10714)

Generated by scripts/run_synth_did.py at 2026-04-30T12:29:43+00:00

Notes

Tax-inequality candidate, swarm-S6 batch 4.

Authored framework. Read the transparency note.