This paper develops a method for solving the identification problem that arises in simultaneous-equation models. It is based on the heteroskedasticity of the structural shocks. For simplicity, I consider heteroskedasticity that can be described as a two-regime process and show that the system is just identified. I discuss identification under general conditions, such as more than two regimes, when common unobservable shocks exist, and situations in which the nature of the heteroskedasticity is misspecified. Finally, I use this methodology to measure the contemporaneous relationship between the returns on Argentinean, Brazilian, and Mexican sovereign bonds—a case in which standard identification methodologies do not apply.

Using unique data on mutual fund portfolios with different investment scopes, we study the extent of international diversification. Mutual funds invest in a surprisingly limited number of stocks—about 100. The number of holdings from a given region declines as the investment scope broadens. Moreover, unexploited gains exist from international diversification. Funds that invest globally could achieve better risk-adjusted returns by adding stocks held by more specialized funds within the same family. These findings are not driven by different sectoral allocations, lack of information or instruments, transaction costs, or different tail risks. Instead, organizational factors might play an important role.