IESET.
Hypotheses·fiscal·flat_tax_reform_growth_panel

Countries that adopted a flat personal-income-tax regime between 1994 and 2012 experienced faster real GDP per capita growth in the decade following reform than matched non-reforming peers, controlling for initial income, institutional quality, and trade openness.

The directional claim is that flat-tax adoption is associated with at least 0.5 percentage points higher annual real GDP per capita growth over the post-reform decade.

SUPPORTEDengine/runs/flat_tax_reform_growth_panel

SUPPORTED — coef=+2.028 (sign matches claim +), p=0.0024

confidence cueThis is a clear pass for the claim as written. It still applies only to this sample, period, and method.

policy briefClear support

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 data clearly moved in the predicted direction. coef=+2.028 (sign matches claim +), p=0.0024

why it matters

This matters because fiscal claims should change belief only when they survive a pre-declared empirical test.

how the test works

It compares 18 country or place units from 1990 to 2023, using a panel fe design, with fixed effects for country and year.

what was measured
What changed
  • Flat tax adopter indicator
  • Years since flat tax
What we checked
  • Real income per capita growth
  • Real income per capita level
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

6 input datasets, 0 unresolved missing series, provenance status: reproducible hash verified.

Results

engine/runs/flat_tax_reform_growth_panel
1007550250199020072023ESTLVALTURUSSRBROUUKR
illustrative sketch · run pending
No coefficients yet. When the model fires, this chart will show real_gdp_per_capita_growth across 18 sampled countries over 1990–2023.
The shapes above are stylised — none of the lines are real data.
Placeholder for flat_tax_reform_growth_panel. Published chart will be generated from engine/runs/flat_tax_reform_growth_panel/chart_data.json.

Pre-registration

pre-registered
first-spec commit 91b4750 · 2026-05-03T09:44:53Z
run generated · 2026-06-29T17:52:21Z

Countries that adopted a flat personal-income-tax regime between 1994 and 2012 experienced faster real GDP per capita growth in the decade following reform than matched non-reforming peers, controlling for initial income, institutional quality, and trade openness. The directional claim is that flat-tax adoption is associated with at least 0.5 percentage points higher annual real GDP per capita growth over the post-reform decade.

Falsification criterion — what would disprove this

set before the run · honoured after

This hypothesis is considered falsified if:

SUPPORTED if β1 (flat-tax indicator) is positive and significant at p<0.10 and the post-reform decade mean growth gap vs synthetic counterfactual is at least 0.3 pp/year. PARTIAL if positive and significant in FE but not in synthetic-control estimates. REFUTED if β1 is negative and significant at p<0.10. INFORMATIVE: excluding Russia and Estonia should not eliminate the positive sign; if it does, the result is driven by two dominant cases.

formal test & threshold
test:      panel_fe_flat_tax_growth_staggered_adoption
threshold: β_flat_tax (GDP pc growth) > 0 at p<=0.10  AND Synthetic-control post-reform gap >= 0.30 pp/yr  AND Ex-Russia-Estonia robustness retains positive sign.

Method

Template
panel_fe
Fixed effects
country, year
Clustering
country
Sample
18 countries · 1990 – 2023
Evidence type
associational

Two-way FE panel with staggered adoption: growth = β0 + β1*flat_tax + β2*years_since + controls + FE. Robustness: (1) exclude Russia and Estonia (dominant early adopters); (2) use synthetic control for each adopter vs matched non-adopters; (3) subsample by OECD vs non-OECD; (4) use Fraser EFW tax-burden sub-index as continuous alternative treatment.

Data

VariableSourceTransform
real_gdp_per_capita_growth
outcome
world_bank_wdi:NY.GDP.PCAP.KD.ZGtier 2
level
real_gdp_per_capita_level
outcome
world_bank_wdi:NY.GDP.PCAP.KDtier 2
log
flat_tax_adopter_indicator
treatment
constructed:indicator = 1 for EST from 1994; LVA from 1997; LTU from 1994; RUS from 2001; SRB from 2003; ROU from 2005; UKR from 200tier 5
indicator
years_since_flat_tax
treatment
constructed:indicator = 1 for EST from 1994; LVA from 1997; LTU from 1994; RUS from 2001; SRB from 2003; ROU from 2005; UKR from 200tier 5
years_since
log_initial_gdp_per_capita
control
world_bank_wdi:NY.GDP.PCAP.KDtier 2
log
institutional_quality
control
wgi:RL.ESTtier 4
level
trade_openness
control
world_bank_wdi:NE.TRD.GNFS.ZStier 2
level
inflation_rate
control
world_bank_wdi:FP.CPI.TOTL.ZGtier 2
level
investment_share_gdp
control
world_bank_wdi:NE.GDI.FTOT.ZStier 2
level

● ready  · ● pending  · ● reconstruct-needed

Detailed result card

Result card — flat_tax_reform_growth_panel

Verdict: SUPPORTED — coef=+2.028 (sign matches claim +), p=0.0024

Pre-registration

  • Claim: Countries that adopted a flat personal-income-tax regime between 1994 and 2012 experienced faster real GDP per capita growth in the decade following reform than matched non-reforming peers, controlling for initial income, institutional quality, and trade openness. The directional claim is that flat-tax adoption is associated with at least 0.5 percentage points higher annual real GDP per capita growth over the post-reform decade.
  • Falsification rule: SUPPORTED if β1 (flat-tax indicator) is positive and significant at p<0.10 and the post-reform decade mean growth gap vs synthetic counterfactual is at least 0.3 pp/year. PARTIAL if positive and significant in FE but not in synthetic-control estimates. REFUTED if β1 is negative and significant at p<0.10. INFORMATIVE: excluding Russia and Estonia should not eliminate the positive sign; if it does, the result is driven by two dominant cases.
  • Falsification test: panel_fe_flat_tax_growth_staggered_adoption

Estimate

  • Method: linearmodels.PanelOLS
  • Coefficient (treatment): +2.028
  • Std error: 0.6635
  • p-value: 0.0024
  • Observations: 418, countries: 17
  • Within R²: -0.519
  • Fixed effects: entity=True, time=True
  • Clustering: country

Variables resolved

  • world_bank_wdi:NY.GDP.PCAP.KD.ZG → real_gdp_per_capita_growth (outcome, publisher=world_bank_wdi, n=13897)
  • world_bank_wdi:NY.GDP.PCAP.KD → real_gdp_per_capita_level (outcome, publisher=world_bank_wdi, n=12104)
  • constructed: indicator = 1 for EST from 1994; LVA from 1997; LTU from 1994; RUS from 2001; SRB from 2003; ROU from 2005; UKR from 2004; BGR from 2008; ALB from 2008; CZE from 2008; SVK from 2004; MKD from 2007; MNE from 2007; HUN from 2012; GEO from 2005; KAZ from 2007; KGZ from 2006; MNG from 2007 → flat_tax_adopter_indicator (treatment, publisher=constructed, n=612)
  • constructed: indicator = 1 for EST from 1994; LVA from 1997; LTU from 1994; RUS from 2001; SRB from 2003; ROU from 2005; UKR from 2004; BGR from 2008; ALB from 2008; CZE from 2008; SVK from 2004; MKD from 2007; MNE from 2007; HUN from 2012; GEO from 2005; KAZ from 2007; KGZ from 2006; MNG from 2007 → years_since_flat_tax (treatment, publisher=constructed, n=612)
  • world_bank_wdi:NY.GDP.PCAP.KD → log_initial_gdp_per_capita (controls, publisher=world_bank_wdi, n=12104)
  • wgi:RL.EST → institutional_quality (controls, publisher=wgi, n=5296)
  • world_bank_wdi:NE.TRD.GNFS.ZS → trade_openness (controls, publisher=world_bank_wdi, n=10714)
  • world_bank_wdi:FP.CPI.TOTL.ZG → inflation_rate (controls, publisher=world_bank_wdi, n=7550)
  • world_bank_wdi:NE.GDI.FTOT.ZS → investment_share_gdp (controls, publisher=world_bank_wdi, n=9870)

Generated by scripts/run_panel_fe.py at 2026-06-29T17:52:21+00:00

Strongest opposing argument

Every hypothesis ships with its charitable opposing argument. The framework earns credibility by handling objections at their strongest, not weakest.

Authored framework. Read the transparency note.