This discussion paper resulted in a publication IN the <a HREF="http://people.few.eur.nl/hkvandijk/PDF/Koop_and_Van_Dijk_2000_JoE_testing_for_integration.pdf">'Journal of Econometrics'</a>, 2000, 97(2), 261-291.<p> In this paper, we make use of state space models to investigate the presence of stochastic trends in economic time series. A model is specified where such a trend can enter either in the...</p>