A major reason that portfolios can

A major reason that portfolios can effectively reduce risk is that combining securities
whose returns do not move together provides diversification. Sometimes a subset of
assets will go up in value at the same time that another will go down in value. The
fact that these may offset each other creates the potential diversification benefit we
attribute to portfolios. However, an important issue is that the co-movement or
correlation pattern of the securities’ returns in the portfolio can change in a manner
unfavorable to the investor. We use historical return data from a set of global indices
to show the impact of changing co-movement patterns.

Results (English) 2:

一个主要的原因，投资组合能有效地降低风险，结合证券
的回报不动起来提供多样化。有时
资产的一个子集将在价值的同时，另一个会跌价。事实上，这些可能的
相互抵消，造成潜在的多样化经营的好处我们
属性组合。不过，一个重要的问题是，在投资组合中的有限的运动或
的证券收益的相关模式可以
不利于投资者转变。我们用历史收益数据从一组全局指数
显示变化的有限的运动模式的影响。