Rational bubbles and fractional integration

In this article we provide evidence for a rational bubble in S\&P 500 stock prices by applying a test for changing persistence under fractional integration proposed by Sibbertsen and Kruse (2007). We find strong evidence for stationary long memory before the estimated change point in 1955 and a unit root afterwards. These results bring two empirical findings in line: on one hand they confirm the previous result of fractional integration and on the other hand they support the hypothesis of a rational bubble.fractional integration, bubbles, changing persistence