'Computes only lambda -- the main part of the test statistic'

def _compute_lambda(self, Y, X):

    n = np.shape(X)[0]
    Y = _adjust_shape(Y, 1)
    X = _adjust_shape(X, self.k_vars)
    b = KernelReg(Y, X, self.var_type, self.model.reg_type, self.bw, defaults=EstimatorSettings(efficient=False)).fit()[1]
    b = b[:, self.test_vars]
    b = np.reshape(b, (n, len(self.test_vars)))
    fct = 1.0
    lam = (((b / fct) ** 2).sum() / float(n))
    return lam
