FA-340 / Statistics / Member archive

Percentile interpolation uses unsorted observation positions · case 05

A percentile depends on input order or jumps to a nearest-rank value instead of the specified interpolated value.

Member previewVariant 5 · 3 implementations · 9 checks per implementation

Case contract

For an integer sample and integer percentile p from 0 through 100, return the reduced Fraction string for linear interpolation at h=(n-1)*p/100 in sorted order. Empty samples and out-of-range p return None.

Why this case matters

Percentile definitions differ across libraries. This case specifies one convention and tests order independence instead of treating all percentile algorithms as interchangeable.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
unordered even-sample median	`"5"`	`"15/2"`	Failed

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