We study active investment skills in relation to returns to scale in the active mutual fund industry. Using a sample of 13,807 funds from sixteen domicile countries investing in forty-two equity markets from 2001 to 2014, we find that they achieve negative trading performance on average, driven mainly by particularly low returns to their trades in US equities. Exploring their investment environment, we find convincing evidence of decreasing returns to scale around the world, especially for the US market. Based on theory of optimal fund size, we estimate the optimal size of the active mutual fund industry. We find that the active mutual fund industry in USA has exceeded the optimal level, whereas in the international markets, there may still be room for further expansion. Consistent with this view, we find that mutual fund managers have been gradually reallocating their assets away from the USA and more into international equity markets.

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减少交易并退出拥挤的市场：国际共同基金的经验教训*

我们研究活跃的共同基金行业中与规模收益相关的活跃投资技巧。我们从2001年至2014年对16个居住于16个居住国的13,807个基金进行了投资，我们发现它们平均取得负交易业绩，这主要是由于其美国股票交易的收益特别低。在探索他们的投资环境时，我们发现令人信服的证据表明，在全球范围内，尤其是在美国市场，规模回报率不断下降。基于最优基金规模理论，我们估算了活跃的共同基金行业的最优规模。我们发现，美国活跃的共同基金行业已经超过了最佳水平，而在国际市场上，仍有进一步扩展的空间。与这种观点一致，