code: function approximateZPercentile(z, alpha=true) {
                // If z is greater than 6.5 standard deviations from the mean
                // the number of significant digits will be outside of a reasonable 
                // range.
                if (z < -6.5)
                  return 0.0;
  
                if (z > 6.5)
                  return 1.0;
  
                let factK    = 1;
                let sum      = 0;
                let term     = 1;
                let k        = 0;
                let loopStop = Math.exp(-23);
                 
                while (Math.abs(term) > loopStop) {
                  term = 0.3989422804 * Math.pow(-1, k) * Math.pow(z, k) / (2 * k + 1) /
                          Math.pow(2, k) * Math.pow(z, k + 1) / factK;
                  sum += term;
                  k++;
                  factK *= k;
                }
  
                sum += 0.5;
  
                return (alpha) ? 1 - sum : sum;
              }
docs: Converts z-score into the probability
  @memberOf util
  @see {@link https://stackoverflow.com/questions/36575743/how-do-i-convert-probability-into-z-score}
  @param {number} z - Number of standard deviations from the mean.
  @returns {number} p  - p-value