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Fractional age survival assumptions: Balducci survival uses the elapsed rather than remaining fraction · case 02

Balducci survival probabilities are too high early in the year.

Member previewVariant 2 · 3 implementations · 12 checks per implementation

Case contract

Input q (per 100000), t as [num, den] in [0,1], assumption udd|cfm|balducci. UDD: tp=1-tq, mu=q/(1-tq); constant force: tp=p^t, mu=-ln p; Balducci: tp=p/(1-(1-t)q), mu=q/(1-(1-t)q). Out-of-range -> 'invalid'; infinite force -> 'infinite force'; other -> 'unknown assumption'. Return [tp, mu] rounded to 8 places.

Why this case matters

Life-table arithmetic compounds across ages, so one misplaced index or assumption shifts every downstream value.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
balducci third of year	`[0.81802313, 0.30028805]`	`[0.89990398, 0.30028805]`	Failed

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