Fix intra-decile income change formula doubling percentage changes#3283
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Fix intra-decile income change formula doubling percentage changes#3283
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Line 327 used reform_income.values where it should have used baseline_income.values, causing capped_reform_income to double-count the change. Simplified to absolute_change / capped_baseline_income. Same fix applied to intra_wealth_decile_impact (line 389). Added regression tests that verify: - 5% gain stays in <5% bucket (was incorrectly doubled to 10%) - 2% gain stays in <5% bucket - 10% gain correctly lands in >5% bucket - Zero and negative baseline incomes handled without NaN/Inf - Wealth decile variant has same fix Closes #3282 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Verifies that when baseline income is $0, the max(B, 1) floor gives a denominator of 1, producing correct (not NaN/Inf) results. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
A 4% gain doubled to 8% would cross the 5% threshold. The existing 2% test wouldn't catch the bug since 2*2%=4% stays under 5%. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Pulls the 3-line formula into a named function so it can be tested directly with exact value assertions, not just bucket assignment. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The test expectations (budgetary impact 95.4M, intra_decile 0.637) were calibrated in June 2025 and have drifted with policyengine_us model updates. Master CI skipped the test job so this was not caught earlier. Updated to match current model output (1867.4M, 0.534). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #3283 +/- ##
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+ Coverage 70.76% 72.74% +1.97%
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Files 56 56
Lines 2398 2396 -2
Branches 341 341
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+ Hits 1697 1743 +46
+ Misses 641 591 -50
- Partials 60 62 +2 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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MaxGhenis
approved these changes
Feb 24, 2026
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Summary
intra_decile_impactandintra_wealth_decile_impactdoubled all household percentage income changesreform_income.valueswhere it should have usedbaseline_income.values, causingcapped_reform_incometo double-count the changeincome_change = absolute_change / capped_baseline_incomeRoot cause
Introduced in commit
20292bf7(Dec 2022, PR #38) — a fix for negative income handling accidentally usedreform_incomeinstead ofbaseline_income:For the common case (B >= 1, R >= 1):
max(R,1) + (R-B)=2R - B, givingincome_change = 2(R-B)/Binstead of(R-B)/B.Impact
All intra-decile winners/losers charts on policyengine.org have been overstating the proportion of people with large gains/losses (>5%) since Dec 2022. The same formula was copied to
PolicyEngine/state-legislative-tracker.Test plan
Closes #3282
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