StDev implementations in C#

stdev.cs

using System;
using System.Collections.Generic;
 
namespace SampleApp
{
    internal class Program
    {
        private static void Main()
        {
            List<double> data = new List<double> {1, 2, 3, 4, 5, 6};
 
            double mean = data.Mean();
            double variance = data.Variance();
            double sd = data.StandardDeviation();
 
            Console.WriteLine("Mean: {0}, Variance: {1}, SD: {2}", mean, variance, sd);
            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }
    }
 
    public static class MyListExtensions
    {
        public static double Mean(this List<double> values)
        {
            return values.Count == 0 ? 0 : values.Mean(0, values.Count);
        }
 
        public static double Mean(this List<double> values, int start, int end)
        {
            double s = 0;
 
            for (int i = start; i < end; i++)
            {
                s += values[i];
            }
 
            return s / (end - start);
        }
 
        public static double Variance(this List<double> values)
        {
            return values.Variance(values.Mean(), 0, values.Count);
        }
 
        public static double Variance(this List<double> values, double mean)
        {
            return values.Variance(mean, 0, values.Count);
        }
 
        public static double Variance(this List<double> values, double mean, int start, int end)
        {
            double variance = 0;
 
            for (int i = start; i < end; i++)
            {
                variance += Math.Pow((values[i] - mean), 2);
            }
 
            int n = end - start;
            if (start > 0) n -= 1;
 
            return variance / (n);
        }
 
        public static double StandardDeviation(this List<double> values)
        {
            return values.Count == 0 ? 0 : values.StandardDeviation(0, values.Count);
        }
 
        public static double StandardDeviation(this List<double> values, int start, int end)
        {
            double mean = values.Mean(start, end);
            double variance = values.Variance(mean, start, end);
 
            return Math.Sqrt(variance);
        }
    }
}