stats.ts

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`d3e4ed26` 2026-10-25 Pavel Safronov	1	/** Mean and a 95% confidence interval's half-width, for paired differences and plain samples. */
	2	export interface Estimate {
	3	mean: number
	4	/** Half the 95% interval: the true mean is within mean ± ci, 19 times in 20. */
	5	ci: number
	6	n: number
	7	}
	8
	9	export function estimate(xs: number[]): Estimate {
	10	const n = xs.length
	11	if (!n) return { mean: 0, ci: 0, n }
	12	const mean = xs.reduce((a, b) => a + b, 0) / n
	13	const variance = n > 1 ? xs.reduce((a, x) => a + (x - mean) ** 2, 0) / (n - 1) : 0
	14	return { mean, ci: 1.96 * Math.sqrt(variance / n), n }
	15	}
	16
	17	/** "+1.2 ± 0.3", or "+1.2 ± 0.3 ✱" when the interval leaves out 0 (a real difference). */
	18	export function signed(e: Estimate, digits = 2): string {
	19	const sign = e.mean > 0 ? '+' : e.mean < 0 ? '−' : ' '
	20	const real = e.n > 1 && Math.abs(e.mean) > e.ci ? ' ✱' : ''
	21	return `${sign}${Math.abs(e.mean).toFixed(digits)} ± ${e.ci.toFixed(digits)}${real}`
	22	}