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arXiv 2103.06476math.STstat.MEstat.MLstat.TH
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时间一致的中心极限理论及渐近置信序列

Time-uniform central limit theory and asymptotic confidence sequences

Ian Waudby-Smith, David Arbour, Ritwik Sinha, Edward H. Kennedy, Aaditya Ramdas

AI总结:

本文提出渐近置信序列的定义与推导方法,利用强不变原理以高斯过程均匀逼近样本均值过程,从而在序贯环境下为观察性研究和随机实验中的平均处理效应提供时间一致的因果推断。

摘要:

基于中心极限定理(CLT)的置信区间是经典统计学的基石。尽管它们仅具有渐近有效性,但由于能在弱假设下进行统计推断,且常常能应用于即使非渐近推断不可行的问题,因此无处不在。本文引入了此类渐近置信区间的时间一致类比,补充了关于置信序列(CS)的文献——置信序列是随时间均匀有效的置信区间序列,它允许在任意停止时间进行有效推断,且不像经典置信区间那样需要预先固定样本量,因此不会因“偷看”数据而受到惩罚。文献中现有的CS是非渐近的,享有有限样本保证,但不具备上述渐近置信区间的广泛适用性。本文为“渐近CS”提供了定义及推导它们的一般方法。渐近CS放弃了非渐近有效性,以换取类似CLT的通用性和(渐近)时间一致的保证。虽然CLT针对固定样本量用高斯分布近似样本均值的分布,我们使用强不变原理(源于Strassen在1960年代的开创性工作)用隐式高斯过程均匀近似整个样本均值过程。作为示例,我们为观察性研究中的平均处理效应(即使在固定时间设定下,非渐近界也基本无法推导)以及随机实验推导了渐近CS,从而在序贯环境中实现因果推断。

英文摘要:

Confidence intervals based on the central limit theorem (CLT) are a cornerstone of classical statistics. Despite being only asymptotically valid, they are ubiquitous because they permit statistical inference under weak assumptions and can often be applied to problems even when nonasymptotic inference is impossible. This paper introduces time-uniform analogues of such asymptotic confidence intervals, adding to the literature on confidence sequences (CS) -- sequences of confidence intervals that are uniformly valid over time -- which provide valid inference at arbitrary stopping times and incur no penalties for "peeking" at the data, unlike classical confidence intervals which require the sample size to be fixed in advance. Existing CSs in the literature are nonasymptotic, enjoying finite-sample guarantees but not the aforementioned broad applicability of asymptotic confidence intervals. This work provides a definition for "asymptotic CSs" and a general recipe for deriving them. Asymptotic CSs forgo nonasymptotic validity for CLT-like versatility and (asymptotic) time-uniform guarantees. While the CLT approximates the distribution of a sample average by that of a Gaussian for a fixed sample size, we use strong invariance principles (stemming from the seminal 1960s work of Strassen) to uniformly approximate the entire sample average process by an implicit Gaussian process. As an illustration, we derive asymptotic CSs for the average treatment effect in observational studies (for which nonasymptotic bounds are essentially impossible to derive even in the fixed-time regime) as well as randomized experiments, enabling causal inference in sequential environments.

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