        self.slope
    }

    /// Standard error of the estimate.
    pub fn standard_error(&self) -> f64 {
        self.standard_error
    }

    fn simple_lr(data: &[(f64, f64)]) -> Result<Self, Error> {
        let n = data.len() as f64;

        let (x, y): (Vec<_,>, Vec<_>) = data.iter().cloned().unzip();
