/**
 * Fisher-Pearson sample skewness (ignores NaNs). Returns NaN when insufficient data.
 * @param source Input array
 * @returns Skewness or NaN
 */
export declare function skew(source: ArrayLike<number>): number;
/**
 * Excess kurtosis (kurtosis - 3) for `source` (ignores NaNs). Returns NaN when insufficient data.
 * @param source Input array
 * @returns Excess kurtosis or NaN
 */
export declare function kurtosis(source: ArrayLike<number>): number;
/**
 * Rolling skewness over a sliding window of length `period`.
 * @param source Input array
 * @param period Window length
 * @returns Float64Array of rolling skewness values
 */
export declare function rollskew(source: ArrayLike<number>, period: number): Float64Array;
/**
 * Rolling excess kurtosis over a sliding window of length `period`.
 * @param source Input array
 * @param period Window length
 * @returns Float64Array of rolling kurtosis values
 */
export declare function rollkurtosis(source: ArrayLike<number>, period: number): Float64Array;