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arXiv 2106.07263stat.MLcs.LG
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在线实验中方差缩减的机器学习

Machine Learning for Variance Reduction in Online Experiments

Princeton University(普林斯顿大学);Facebook

Yongyi Guo, Dominic Coey, Mikael Konutgan, Wenting Li, Chris Schoener, Matt Goldman

摘要:

我们考虑在随机对照试验中通过使用与结果相关但与治疗无关的协变量来减少方差的问题。我们提出了一个机器学习回归调整的处理效应估计,我们称之为MLRATE。MLRATE使用结果的机器学习预测器来减少估计方差。它采用交叉拟合,以避免过度拟合的偏见,我们证明了一致性和渐近正态性在一般条件下。MLRATE对来自机器学习步骤的不良预测具有鲁棒性:如果预测与结果不相关,则估计量的性能渐近地不比标准均值差估计量差,而如果预测与结果高度相关,则效率增益很大。在A/A测试中,对于Facebook实验中通常监测的一组48个结果指标,估计量的方差比简单的均值差估计量低70%以上,比仅针对结果的实验前值进行调整的常见单变量过程低约19%。

英文摘要:

We consider the problem of variance reduction in randomized controlled trials, through the use of covariates correlated with the outcome but independent of the treatment. We propose a machine learning regression-adjusted treatment effect estimator, which we call MLRATE. MLRATE uses machine learning predictors of the outcome to reduce estimator variance. It employs cross-fitting to avoid overfitting biases, and we prove consistency and asymptotic normality under general conditions. MLRATE is robust to poor predictions from the machine learning step: if the predictions are uncorrelated with the outcomes, the estimator performs asymptotically no worse than the standard difference-in-means estimator, while if predictions are highly correlated with outcomes, the efficiency gains are large. In A/A tests, for a set of 48 outcome metrics commonly monitored in Facebook experiments the estimator has over 70% lower variance than the simple difference-in-means estimator, and about 19% lower variance than the common univariate procedure which adjusts only for pre-experiment values of the outcome.

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