平方根之外：市场冲击对规模和参与率的对数依赖性证据
Beyond the square root: Evidence for logarithmic dependence of market impact on size and participation rate
摘要：
我们对2007年至2009年美国股市执行的大额订单（元订单）的市场冲击进行了广泛的实证研究。我们发现，平方根市场冲击公式，这是广泛使用的行业和支持以前发表的研究，提供了一个很好的适合只有大约两个数量级的订单大小。对数函数形式更好地拟合数据，在几乎五个数量级上提供良好的拟合。我们引入了“影响面”的概念来模拟作为持续时间和元序参与率的函数的影响，再次发现对数依赖性。我们发现，在执行过程中的价格轨迹偏离市场冲击，一个明确的指示，非VWAP执行。令人惊讶的是，我们发现有时价格在执行结束前就开始恢复。最后，我们表明，虽然平均影响放松到约2/3的峰值影响，精确的渐近值的价格取决于参与率和持续时间的元序。我们提出的证据表明，这可能是由于元目之间的羊群现象。
英文摘要：
We make an extensive empirical study of the market impact of large orders (metaorders) executed in the U.S. equity market between 2007 and 2009. We show that the square root market impact formula, which is widely used in the industry and supported by previous published research, provides a good fit only across about two orders of magnitude in order size. A logarithmic functional form fits the data better, providing a good fit across almost five orders of magnitude. We introduce the concept of an "impact surface" to model the impact as a function of both the duration and the participation rate of the metaorder, finding again a logarithmic dependence. We show that during the execution the price trajectory deviates from the market impact, a clear indication of non-VWAP executions. Surprisingly, we find that sometimes the price starts reverting well before the end of the execution. Finally we show that, although on average the impact relaxes to approximately 2/3 of the peak impact, the precise asymptotic value of the price depends on the participation rate and on the duration of the metaorder. We present evidence that this might be due to a herding phenomenon among metaorders.
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