Fix D6: match Clojure two-proportion test formula (+1 pseudocount)#2520
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Fix D6: match Clojure two-proportion test formula (+1 pseudocount)#2520jucor wants to merge 1 commit into
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Pull request overview
This PR updates Delphi’s representativeness z-score computation to match the Clojure stats/two-prop-test behavior by switching two_prop_test (and its vectorized variant) from proportion inputs to raw count inputs and applying a +1 pseudocount to all four parameters.
Changes:
- Changed
two_prop_test/two_prop_test_vectorizedsignatures to accept raw counts(succ_in, succ_out, pop_in, pop_out)and implemented the +1 pseudocount pooled z-test formula. - Updated scalar and vectorized call sites to pass raw counts (
na/nd/nsand “other” counts) instead of proportions. - Updated and expanded unit + discrepancy tests and documentation to reflect the new signature and intended Clojure parity.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
delphi/polismath/pca_kmeans_rep/repness.py |
Implements the new count-based two-proportion test (scalar + vectorized) and updates callers. |
delphi/tests/test_repness_unit.py |
Updates unit tests for the new two_prop_test / vectorized signature and expectations. |
delphi/tests/test_old_format_repness.py |
Updates old-format API tests for the new two_prop_test signature. |
delphi/tests/test_discrepancy_fixes.py |
Rewrites D6 tests to assert parity with a Clojure-reference implementation and adds blob-injection coverage. |
delphi/docs/PLAN_DISCREPANCY_FIXES.md |
Marks D6 as done in the discrepancy plan. |
delphi/docs/CLJ-PARITY-FIXES-JOURNAL.md |
Adds a journal entry documenting the D6 parity work and test updates. |
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| if pop_in == 0 or pop_out == 0: | ||
| return 0.0 |
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| # Handle edge cases: pop_in=0 or pop_out=0 → 0, pi_hat=1 → 0 | ||
| z = z.where((pop_in > 0) & (pop_out > 0), 0.0) |
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| # Edge cases: pop=0 → 0 | ||
| assert two_prop_test(5, 5, 0, 100) == 0.0 | ||
| assert two_prop_test(5, 5, 100, 0) == 0.0 |
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| # Edge cases: pop=0 → 0 | ||
| assert two_prop_test(5, 5, 0, 100) == 0.0 | ||
| assert two_prop_test(5, 5, 100, 0) == 0.0 | ||
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| """Edge cases: n=0 should return 0, pi_hat=1 should return 0.""" | ||
| # n=0 cases | ||
| check.equal(two_prop_test(5, 5, 0, 10), 0.0) | ||
| check.equal(two_prop_test(5, 5, 10, 0), 0.0) | ||
| # Both zero | ||
| check.equal(two_prop_test(0, 0, 0, 0), 0.0) | ||
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## Summary The Python `two_prop_test` used a standard two-proportion z-test with no pseudocounts, while Clojure's `stats/two-prop-test` (stats.clj:18-33) adds +1 to all four inputs (`succ-in`, `succ-out`, `pop-in`, `pop-out`) via `(map inc ...)` before computing the pooled z-test. This Laplace smoothing regularizes z-scores for small group sizes, which are common in Polis conversations. ## Changes - **Signature change**: `two_prop_test(p1, n1, p2, n2)` (proportions) → `two_prop_test(succ_in, succ_out, pop_in, pop_out)` (raw counts) - **Formula**: Standard pooled z-test on pseudocount-adjusted values: `pi1 = (succ_in+1)/(pop_in+1)`, `pi_hat = (s1+s2)/(p1+p2)` - **Callers updated**: Both scalar (`add_comparative_stats`) and vectorized (`compute_group_comment_stats_df`) now pass raw counts matching Clojure's `(stats/two-prop-test (:na in-stats) (sum :na rest-stats) (:ns in-stats) (sum :ns rest-stats))` (repness.clj:97-100) ## Affected output fields - `rat` (agree representativeness test z-score) - `rdt` (disagree representativeness test z-score) - `agree_metric`, `disagree_metric` (downstream of rat/rdt) ## Test plan - [x] Targeted D6 tests pass (formula, edge cases, regularization effect) - [x] Full test suite passes (excluding DynamoDB/MinIO tests) - [x] Private dataset tests pass (--include-local) - [x] Golden snapshots re-recorded for all 7 datasets 🤖 Generated with [Claude Code](https://claude.com/claude-code) ## Squashed commits - RED: add D6 blob injection test (two_prop_test vs Clojure repness-test) - Fix D6: match Clojure two-proportion test formula (+1 pseudocount) - Plan: add D6 PR number and stack position to cross-reference commit-id:23c03d70
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Summary
The Python
two_prop_testused a standard two-proportion z-test with no pseudocounts,while Clojure's
stats/two-prop-test(stats.clj:18-33) adds +1 to all four inputs(
succ-in,succ-out,pop-in,pop-out) via(map inc ...)before computingthe pooled z-test. This Laplace smoothing regularizes z-scores for small group sizes,
which are common in Polis conversations.
Changes
two_prop_test(p1, n1, p2, n2)(proportions) →two_prop_test(succ_in, succ_out, pop_in, pop_out)(raw counts)pi1 = (succ_in+1)/(pop_in+1),pi_hat = (s1+s2)/(p1+p2)add_comparative_stats) and vectorized(
compute_group_comment_stats_df) now pass raw counts matching Clojure's(stats/two-prop-test (:na in-stats) (sum :na rest-stats) (:ns in-stats) (sum :ns rest-stats))(repness.clj:97-100)
Affected output fields
rat(agree representativeness test z-score)rdt(disagree representativeness test z-score)agree_metric,disagree_metric(downstream of rat/rdt)Test plan
🤖 Generated with Claude Code
Squashed commits
commit-id:23c03d70
Stack: