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The share of comparable pairs a set of scores orders correctly, a tie counted one half.

public static double Index(ReadOnlySpan<double> eventTimes, ReadOnlySpan<double> predictedScores)

public static double Index(ReadOnlySpan<double> eventTimes, ReadOnlySpan<double> predictedScores, ReadOnlySpan<bool> eventObserved)

The first overload reads every time as an observed event, lifelines' event_observed=None.

Parameters — eventTimes holds one duration per subject. predictedScores holds one score per subject, higher for a longer predicted survival. eventObserved holds one flag per subject, true where its duration ends in the event.

Returns — the concordance index, between zero and one, a half for scores that carry no information.

Exceptions — ArgumentException when the spans differ in length, a time or a score is NaN, or no pair is comparable, where lifelines raises ZeroDivisionError.

Example — a censored subject is compared only against the events before it.

using Lodestar.Survival;

double c = Concordance.Index([1, 2, 3, 4, 5], [1.5, 1.0, 3.5, 4.0, 6.0], [true, true, false, true, true]);

double index = c;   // => 0.875

Remarks — a pair is comparable when the shorter duration ends in an event, against any later duration and against a censoring at the same duration; two events at one duration are not comparable. The pair is concordant when the shorter duration carries the lower score, and a tie in the scores counts one half. A hazard or a risk score orders the other way, so it is passed negated, as lifelines asks; CoxSummary.ConcordanceIndex is this index on the negated linear predictor. The walk sorts once and counts through a Fenwick tree, n log n in the subjects.

Applies to — net10.0, netstandard2.0.

See also — Concordance, CoxSummary.