Lodestar.Stats 0.2.0. This page is frozen at that release. Read the current documentation for what main says now. A link to a decision or a migration page follows main, and leaves the archive.

Hypothesis testing

Lodestar.Stats answers one question in ten forms: is this difference more than noise?

Which test

you have	and you assume	use
two independent samples	roughly normal	TTest.Independent
two independent samples	nothing about the shape	MannWhitney.Test
the same subjects measured twice	roughly normal differences	TTest.Paired
the same subjects measured twice	nothing about the shape	Wilcoxon.Paired
counts in categories	a stated expected distribution	ChiSquare.GoodnessOfFit
a contingency table	cells large enough for the approximation	ChiSquare.Contingency
a 2×2 table with small cells	nothing	FisherExact.Test
two samples, whole distributions	nothing	KolmogorovSmirnov.TwoSample
three or more groups	roughly normal, similar spread	OneWayAnova.Test
three or more groups	nothing about the shape	KruskalWallis.Test
one sample, and a normality assumption to check	nothing	ShapiroWilk.Test
many p-values at once	nothing	MultipleComparisons

What a p-value is, and is not

A p-value is the probability of seeing a difference at least this large if the null hypothesis is true. It is not the probability that the null hypothesis is true, and it is not the probability that your result is a fluke. A p-value of 0.03 does not mean there is a 3 % chance you are wrong.

Two consequences worth acting on:

• 0.049 and 0.051 are the same evidence. The threshold is a convention, not a discovery. Report the number.
• Twenty tests at 5 % produce one significant result by chance. That is what MultipleComparisons is for, and it is not optional once you are testing more than a couple of things.

The step-up procedure below is MultipleComparisons.BenjaminiHochberg, the one most people reach for first:

using Lodestar.Stats;

double[] pValues = [0.001, 0.008, 0.039, 0.041, 0.042];

double[] adjusted = MultipleComparisons.BenjaminiHochberg(pValues);

bool stillSignificant = adjusted[0] < 0.05;   // => True

One default that is not scipy's

TTest.Independent defaults to Welch's test; scipy.stats.ttest_ind defaults to Student's. Pooling the two variances is only correct when the populations really share one, which is an assumption most callers have not checked. Pass Variance.Equal for scipy's default. Everything else in this package matches scipy.stats 1.18.0 exactly, and the equivalence table is the row-by-row map, including the handful of places one call refuses rather than answering — a NaN, a warning, or a number a caller did not ask for.

Exact and asymptotic

Three tests carry both an exact null distribution and a normal approximation to it, selected by ExactMethod:

• Auto — exact for a small, untied sample; asymptotic otherwise. What scipy's method='auto' does, and the same thresholds.
• Exact — always the exact distribution. On tied data the number is only approximate, because ties break the equal-probability argument the enumeration rests on; scipy computes there too rather than refusing, and so does this.
• Asymptotic — always the normal approximation, whatever the sample size.

The branch changes the number, not just the running time, which is why it is a parameter and not a hidden optimisation. Each of the three tests also refuses ExactMethod.Exact past its own size bound — the exact table is O(n·m) or worse to build, and Auto never crosses that bound on its own, falling back to the asymptotic answer instead. The three reference pages (MannWhitney.Test, Wilcoxon.Paired, KolmogorovSmirnov.TwoSample) each state their own bound, because it is not the same number twice.

No maintained incumbent to compare against

MathNet.Numerics 5.0.0 (2022-04-03, 74.7M downloads) is the dominant third-party numerical library for .NET, and it ships probability distributions and descriptive statistics — no hypothesis tests. Accord.Statistics 3.8.0, the one .NET library that did carry them, was last published on 2017-10-19; its framework, accord-net/framework (4.5k stars), was archived by its owner on 2020-11-19. ML.NET does prediction: a t-test exists only in Azure ML Studio (classic), a retired hosted product, and Mann-Whitney only in Kusto/KQL — neither is a .NET library a project can reference. There is nothing maintained to benchmark against, which is itself the finding, the same shape as Lodestar.Conformal's survey — but unlike Lodestar.Conformal's case, Accord.Statistics is still installable, and #442's own constraint asks for a named .NET incumbent where one exists at all. TTest.Independent, MannWhitney.Test and ChiSquare.Contingency are benchmarked and cross-checked against it in bench/README.md and docs/guides/performance.md — archived is not the same as absent, and this package's own oracle discipline means the comparison is also a second opinion on scipy, not only a timing.