Ok you have got your answer. I would suggest an alternate approach with Linq goodies and extension methods.
public static double StandardDeviation(this ICollection<double> values)
{
return Math.Sqrt(values.Variance());
}
public static double Variance(this ICollection<double> values)
{
if (values.Count == 0)
return 0;
var avg = values.Average();
return values.Select(x => Math.Pow(x - avg, 2)).Sum() / values.Count;
}
Call it like:
var variance = numbers.Variance(); //or so