Method variance

libraries/Statistic/Statistic.h:200–204

useStdDev must be true to use next three all return NAN if count == zero

  // useStdDev must be true to use next three
  // all return NAN if count == zero
  value_type variance() const {
    if (!_useStdDev) return NaN;
    if (_cnt == 0) return NaN; // prevent DIV0 error
    return _extra.ssqdif() / _cnt;
  }


  // Population standard deviation