Linear regression model outlier detector

LinearRegressionModel.IsOutlier.cs

public bool IsOutlier(double radius, double x, double y)
{
    double yHat = GetValue( x );
    double studentizedResidue = Math.Abs(y - yHat) / Math.Sqrt( GetResidualVariance() );

    return studentizedResidue > radius;
}

private double GetResidualVariance()
{
    return GetRSS() / (count - 2);
}

private double GetRSS()
{
    return  beta * beta * sumXX
            -2 * beta * sumXY
            +2 * alpha * beta * sumX
            +sumYY
            -2 * alpha * sumY
            +alpha * alpha * count;
                    
}