Of course, even looking at these countries entails selection bias, for it excludes countries without price data for much of the twentieth century, notably China and Russia, where communist revolutions terminated the stock markets, resulting in -100% returns for investors. The particular problems that prevented us from observing the returns on these stock markets will never be repeated, but it is wrong to assume that problems of that scale will not recur.
当然，即使对这些国家的观察也是带着选择偏见的，因为这种观察将那些没有二十世纪价格数据的国家排除在外，尤其是中国和俄罗斯，那里的共产主义革命结束了股票市场，结果投资者全盘皆输。阻止我们观察这些股票市场回报率问题的障碍永远也不会再出现了，但是如果以为那样的问题再也不可能重新发生，那就错了。