Testing the hypothesis that international equity market correlation increases in volatile times is a difficult exercise and misleading results have often been reported in the past because of a spurious relationship between correlation and volatility. This paper focuses on extreme correlation, that is to say the correlation between returns in either the negative or positive tail of the multivariate distribution. Using ldquo;extreme value theoryrdquo; to model the multivariate distribution tails, we derive the distribution of extreme correlation for a wide class of return distributions. Using monthly data on the five largest stock markets from 1958 to 1996, we reject the null hypothesis of multivariate normality for the negative tail, but not for the positive tail. We also find that correlation is not related to market volatility per se but to the market trend. Correlation increases in bear markets, but not in bull markets.

The co-movement of international equity markets in different return environments is examined using estimates of realized correlation and volatility. Using a simple ordinary least squares (OLS) regression framework, correlations are shown to be similarly elevated in periods characterized by extreme returns in both up and down markets, which contradicts a body of extant research that finds correlations increase in down markets but not in up markets. In contrast, volatility is much greater in down markets than in up markets. This suggests that it is not a lack of diversification that matters for comparative performance in bear markets, but rather the relative magnitude of negative returns typically experienced during such periods.

Benefits to portfolio diversification depend crucially on correct correlation estimates, hence it is of great importance to both risk management and portfolio optimisation that the exact nature of the correlation structure between international financial assets is understood. Recent discussion on the correlation of international equity returns has focussed on the issue of whether extreme movements in international financial markets are more highly correlated than usual returns. This implies a reduction in the benefits from portfolio diversification since extreme returns are more likely to occur with greater simultaneity. Using the Value-at-Risk methodology we are able to measure the quantile correlation structure implicit in international asset returns in a simple manner without having to resort to fully parametric modelling. We illustrate that the extraction of the quantile covariance structure from this quantile correlation structure is non-trivial. Using daily data on stock market indices for a variety of countries we observe how the correlation and covariance structure changes as we move into the tails of the return distribution. We find for extreme stock market movements the benefits to international diversification are significantly curtailed even after discarding spurious correlation changes.