Reconciling to Mack papers

[henrydingliu]

Summary of Changes

restoring mack calculations incorrectly changed in #952
expanded docstrings to avoid future confusion
added definitive reconciliation to Mack94 and Mack97
indirectly resolves un-executed but would-fail doctests

Related GitHub Issue(s)

refers #1093

Additional Context for Reviewers

• I passed tests locally for both code (uv run pytest) and documentation changes (uv run jb build docs --builder=custom --custom-builder=doctest)

---

Note

Medium Risk
Changes core Mack stochastic quantities used by Development and MackChainladder; incorrect sigma would affect reserve uncertainty, but new paper reconciliation tests reduce regression risk.

Overview
Restores Mack (1997) sigma_ in WeightedRegression for through-origin OLS by setting sigma to sqrt(mse) instead of the prior formula tied to std_err and mse_denom, which had diverged from the papers (see #952). Docstrings and typing on WeightedRegression are expanded so sigma_ is documented as Mack’s process standard deviation, distinct from regression noise.

Adds regression tests that compare Development + MackChainladder outputs to published tables in Mack (1994) and Mack (1997) (sigma, LDF standard errors, IBNR standard errors). Removes the standalone test_sigma1 development test that only checked equality across averaging methods.

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[github-actions]

Pyright Type Completeness

View the full pyright --verifytypes output for this commit

Project (full chainladder package, at this PR's head): 15.0% of exported symbols fully typed (191 / 1270)

	Known	Ambiguous	Unknown	Total
Project (head)	191	110	969	1270

Other symbols referenced but not exported by chainladder: 13

	Known	Ambiguous	Unknown	Total
Other (head)	3	1	9	13

Symbols without documentation:

• Functions without docstring: 310
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): 46.2% fully typed (6 / 13); 1 no longer exported

	Known	Ambiguous	Unknown	Total
Patch	6	5	2	13

Patch symbol details

Symbol	Status	Change
chainladder.methods.tests.test_mack.test_mack1994_hardcode	❌ unknown	new
chainladder.methods.tests.test_mack.test_mack1997_hardcode	❌ unknown	new
chainladder.utils.weighted_regression.WeightedRegression.__init__	✅ known	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.average	✅ known	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.axis	✅ known	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.exponent_	⚠️ ambiguous	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.sigma_	⚠️ ambiguous	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.std_err_	⚠️ ambiguous	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.thru_orig	✅ known	changed (was ⚠️ ambiguous)
chainladder.utils.weighted_regression.WeightedRegression.w	⚠️ ambiguous	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.x	⚠️ ambiguous	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.xp	✅ known	changed (was ❌ unknown)
chainladder.utils.weighted_regression.WeightedRegression.y	✅ known	changed (was ❌ unknown)
chainladder.development.tests.test_development.test_sigma1	—	no longer exported (was ❌ unknown)

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.76%. Comparing base (6c9ce99) to head (97ab6d6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1096      +/-   ##
==========================================
+ Coverage   90.48%   90.76%   +0.28%     
==========================================
  Files          91       91              
  Lines        5289     5287       -2     
  Branches      671      671              
==========================================
+ Hits         4786     4799      +13     
+ Misses        359      346      -13     
+ Partials      144      142       -2     

Flag	Coverage Δ
unittests	90.76% <100.00%> (+0.28%)	⬆️

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