z_score.js

/**
 * The [Z-Score, or Standard Score](http://en.wikipedia.org/wiki/Standard_score).
 *
 * The standard score is the number of standard deviations an observation
 * or datum is above or below the mean. Thus, a positive standard score
 * represents a datum above the mean, while a negative standard score
 * represents a datum below the mean. It is a dimensionless quantity
 * obtained by subtracting the population mean from an individual raw
 * score and then dividing the difference by the population standard
 * deviation.
 *
 * The z-score is only defined if one knows the population parameters;
 * if one only has a sample set, then the analogous computation with
 * sample mean and sample standard deviation yields the
 * Student's t-statistic.
 *
 * @param {number} x
 * @param {number} mean
 * @param {number} standardDeviation
 * @return {number} z score
 * @example
 * zScore(78, 80, 5); // => -0.4
 */
function zScore(x, mean, standardDeviation) {
    return (x - mean) / standardDeviation;
}

export default zScore;