public static double Stdev(this IEnumerable<double> data)
{
if (data.Count() < 2)
return 0;
double avg = data.Average();
double numerator = 0;
foreach (double d in data)
numerator += (d - avg) * (d - avg);
double variance = numerator / (double)(data.Count() - 1);
return Math.Sqrt((double)variance);
}