Long Memory and Structural Breaks in the Spanish Stock Market Index

It is well known that the Spanish stock market index (IBEX 35) exhibits unit roots. However, the implications of possible structural breaks in this series have not been deeply investigated. In this paper, we show that, when including a break at the beginning of 1998, the order of integration of the series becomes slightly smaller, strengthening the evidence of mean-reverting behaviour. When the break date is supposed to be unknown, it is found to be January 1998, with both subsamples still being characterised by a high degree of persistence.