/** Alternative hypothesis direction. */
export type TTestPowerAlternative = 'two-sided' | 'larger' | 'smaller';
/** Options for `tTestPower`. */
export interface TTestPowerOptions {
    /**
     * `'power'` (default): the second positional argument is `nobs` (per-group
     * sample size) and the function returns the power.
     *
     * `'nobs'`: the second positional argument is instead read as the *target
     * power*, and the function solves (by bisection) for the per-group `nobs`
     * (continuous, matching statsmodels' own continuous solver) needed to reach
     * it.
     */
    solveFor?: 'power' | 'nobs';
    /** Default `'two-sided'`. */
    alternative?: TTestPowerAlternative;
}
/**
 * Statistical power of a two-sample t-test with equal group sizes.
 *
 * @param effectSize - Standardized effect size (Cohen's d)
 * @param nobsOrPower - Per-group sample size (`solveFor: 'power'`, the
 *   default) or the target power to solve for (`solveFor: 'nobs'`)
 * @param alpha - Significance level
 * @param opts - `solveFor` (default `'power'`), `alternative` (default `'two-sided'`)
 * @returns The power (default) or the required per-group `nobs` (`solveFor: 'nobs'`)
 *
 * @example
 * tTestPower(0.5, 64, 0.05); // ~0.80146 (statsmodels tt_ind_solve_power)
 * tTestPower(0.5, 0.8, 0.05, { solveFor: 'nobs' }); // ~63.77 (per-group nobs for 80% power)
 */
export declare function tTestPower(effectSize: number, nobsOrPower: number, alpha: number, opts?: TTestPowerOptions): number;
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