/** Return the arithmetic mean of `values`.
 *
 *  Returns `NaN` for an empty array. No allocation beyond the accumulator.
 */
export declare function mean(values: Readonly<number[]>): number;
/** Return the median of `values`.
 *
 *  Allocates a sorted copy — does not mutate the input. Returns `NaN` for an
 *  empty array.
 */
export declare function median(values: Readonly<number[]>): number;
/** Return the population standard deviation of `values`.
 *
 *  Returns `NaN` for an empty array.
 */
export declare function standardDeviation(values: Readonly<number[]>): number;
/** Return the population variance of `values`.
 *
 *  Returns `NaN` for an empty array, `0` for a single element.
 */
export declare function variance(values: Readonly<number[]>): number;
/** Return the weighted average of `values` using `weights`.
 *
 *  Each `values[i]` is weighted by `weights[i]`. The arrays must have the same
 *  length. Returns `NaN` for an empty array or if total weight is `0`. Throws
 *  if `values.length !== weights.length`.
 */
export declare function weightedAverage(values: Readonly<number[]>, weights: Readonly<number[]>): number;
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