code: func SampleVariance(values []int64) float64 {
  	if 0 == len(values) {
  		return 0.0
  	}
  	m := SampleMean(values)
  	var sum float64
  	for _, v := range values {
  		d := float64(v) - m
  		sum += d * d
  	}
  	return sum / float64(len(values))
  }
docs: // SampleVariance returns the variance of the slice of int64.