text: /**
   * 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;
  