/**
 * Calculates the required sample size for a study.
 * @param alpha - The significance level used in the hypothesis test.
 * @param power - The probability of correctly rejecting the null hypothesis.
 * @param sd - The standard deviation of the population.
 * @param effect - The effect size of interest.
 * @returns The required sample size.
 */
export declare function sampleSize(alpha: number, power: number, sd: number, effect: number): number;
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