def _calc_damping(mod_reducs, x_2, x_2_mean, x_3, x_3_mean):
        """Compute the damping ratio using Equation (16)."""
        # Mean values of the predictors
        x_1_mean = -1.0
        x_1 = np.log(np.log(1 / mod_reducs) + 0.103)

        ones = np.ones_like(mod_reducs)
        x = np.c_[ones, x_1, x_2, x_3, (x_1 - x_1_mean) * (x_2 - x_2_mean), (
            x_2 - x_2_mean) * (x_3 - x_3_mean)]
        c = np.c_[2.86, 0.571, -0.103, -0.141, 0.0419, -0.240]

        ln_damping = (c * x).sum(axis=1)
        return np.exp(ln_damping) / 100.