There exist a variety of reasons for the failure to find a unique
cointegrating relationship between economic time series where one
would normally be expected on the basis of economic theory. Among
these are the testing procedure, the span of the data set, the choice
of lag length in generating the test statistic, the presence of
structural breaks, and the presence of cointegration only beyond some
threshold. We propose the concept of regime-sensitive cointegration
whereby the underlying series need not be cointegrated at all times.
We show that cointegration can be switched off when a common
stochastic trend is added. Alternatively, cointegration can be
switched on or off because series normally believed to contain a unit
actually do not. This implies that a linear combination of such
variables need not be cointegrated. To illustrate the concept
empirically, we test the hypothesis of interest-rate parity, and
related hypotheses, using daily Eurorates for the United States and
Canada.