A Bayesian Inference Approach to Testing Mean Reversion in the Swedish Stock Market

In this paper we use a Bayesian approach to test for mean reversion in the Swedish stock market on monthly data 1918-1998. By simply account for the heteroscedasticty of the data with a two state hidden Markov model of normal distributions and taking estimation bias into account via Gibbs sampling we can find no support of mean reversion. This is a contradiction to previous result from Sweden. Our findings suggest that the Swedish stock market can be characterized by two regimes, a tranquil and a volatile, and within the regimes the stock market is random. This finding of randomness is in line with recent evidence for the U.S stock market.