/**
 * Calculate the Pearson correlation coefficient between two arrays
 * @param x - First array of numbers
 * @param y - Second array of numbers
 * @returns Correlation coefficient (-1 to 1)
 * @example
 * correlationCoefficient([1, 2, 3, 4, 5], [2, 4, 6, 8, 10]); // 1 (perfect positive correlation)
 * correlationCoefficient([1, 2, 3, 4, 5], [5, 4, 3, 2, 1]); // -1 (perfect negative correlation)
 * correlationCoefficient([1, 2, 3, 4, 5], [1, 1, 1, 1, 1]); // 0 (no correlation)
 */
export declare const correlationCoefficient: (x: number[], y: number[]) => number;