public double GetExcess(int index1, int index2, int row)
{
EnsureNotEmpty($"Can not calculate excess. Series {this.name} is empty.");
EnsureIndexInRange(index1,index2);
double sd = GetStdDev(index1, index2, row);
return sd == 0 ? 0 : GetMoment(4, index1, index2, row)/Math.Pow(sd, 4);
}