code: function sample_variance(x) {
          // The variance of no numbers is null
          if (x.length <= 1) return null;
  
          var sum_squared_deviations_value = sum_nth_power_deviations(x, 2);
  
          // Find the mean value of that list
          return sum_squared_deviations_value / (x.length - 1);
      }
docs: # [variance](http://en.wikipedia.org/wiki/Variance)  is the sum of squared deviations from the mean  depends on `sum_nth_power_deviations`