¹⁰It is plausible, however, to suppose that these parameters are likely to change only gradually over time. Thus, any change in the cointegrating vector is likely to be gradual. Under these circumstances, an estimation method that allows for the cointegrating vetor to evolve gradually might actually perform reasonably well; to see an attempt at an estimation along these lines, see the SMART estimation method explored in Aron, Duca, Muellbauer, Murata, and Murphy (2008). It would be interesting to test how well this method performs under plausible assumptions about the degree of drift in the coefficients on the cointegrating vector, but such an excercise is beyond the scope of the present paper.