How do I calculate the mean square error

Question

I have the following code that I managed to piece together:

private void CalcMSE(List<Point> data)
{
    double sum = 0.0;

       foreach (Point item in data)
       {
          double difference = item.m_x - item.m_y;
          sum = sum + difference * difference;
       } 
    double mse = sum / x;  //<-- Don't know what x should be!
    Console.WriteLine("The mean square error is {0}",mse) ;
}

the inputs are :

point.m_x = 3;
point.m_y = 1;
pointList.Add(point);

point.m_x = 4;
point.m_y = 4;
pointList.Add(point);

point.m_x = 5;
point.m_y = 6;
pointList.Add(point);

point.m_x = 6;
point.m_y = 6;
pointList.Add(point);

point.m_x = 8;
point.m_y = 10;
pointList.Add(point);

According to those in the know the MSE should be 0.77 and MSR 40.89

But I have no idea what the "formula" for x is (see code comment).

Can anyone assist me who knows anything about linear regression?

here's what the ouputs should be

Answer 1

First of all, I think you should always create a new point before adding to the list point = new Point(x,y) , I don't think list.add creates a copy.

as for the x, I think data.Count() will do