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arXiv 2201.10208stat.MEmath.STstat.MLstat.TH
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半监督分位数估计:高维场景下的鲁棒高效推断

Semi-Supervised Quantile Estimation: Robust and Efficient Inference in High Dimensional Settings

Abhishek Chakrabortty, Guorong Dai, Raymond J. Carroll

AI总结:

针对半监督高维分位数估计场景,提出结合灵活插补策略与去偏步骤的半监督估计量,兼具鲁棒性与效率提升,理论与实验均验证其性能优势。

摘要:

我们研究半监督场景下的分位数估计问题,该场景具备两类可用数据集:(i)规模较小或中等的标记数据集,包含响应变量的观测值以及一组可能为高维的协变量;(ii)规模大得多的无标记数据集,仅观测到协变量。我们基于这两类数据集提出了一族响应变量分位数的半监督估计量,相较于监督估计量(即来自标记数据的样本分位数),能够提升估计精度。\n这些估计量在估计方程中采用灵活的插补策略,同时搭配去偏步骤,可对插补模型的误设保持完全鲁棒性。此外,我们采用单步更新策略,既便于方法实现,也能处理分位数估计方程的非线性特性带来的复杂度。在温和假设下,我们的估计量对冗余插补模型的选择具有完全鲁棒性,具体表现为始终保持根n一致性与渐近正态性,同时相对于监督估计量具备更高的效率。若响应变量与协变量的关系通过插补模型被正确设定,这些估计量还能达到半参数最优。\n作为冗余插补函数估计的示例,我们考虑了基于高维协变量的低维(且可能为估计得到的)变换的核平滑类估计量,并推导了其在高维场景下一致收敛速率的新结果,涉及由函数族索引的响应变量以及降维技术的使用,这些结果本身也具有独立研究价值。模拟数据与真实数据上的数值结果均证实,我们的半监督方法在估计与推断两方面均表现出更优性能。

英文摘要:

We consider quantile estimation in a semi-supervised setting, characterized by two available data sets: (i) a small or moderate sized labeled data set containing observations for a response and a set of possibly high dimensional covariates, and (ii) a much larger unlabeled data set where only the covariates are observed. We propose a family of semi-supervised estimators for the response quantile(s) based on the two data sets, to improve the estimation accuracy compared to the supervised estimator, i.e., the sample quantile from the labeled data. These estimators use a flexible imputation strategy applied to the estimating equation along with a debiasing step that allows for full robustness against misspecification of the imputation model. Further, a one-step update strategy is adopted to enable easy implementation of our method and handle the complexity from the non-linear nature of the quantile estimating equation. Under mild assumptions, our estimators are fully robust to the choice of the nuisance imputation model, in the sense of always maintaining root-n consistency and asymptotic normality, while having improved efficiency relative to the supervised estimator. They also attain semi-parametric optimality if the relation between the response and the covariates is correctly specified via the imputation model. As an illustration of estimating the nuisance imputation function, we consider kernel smoothing type estimators on lower dimensional and possibly estimated transformations of the high dimensional covariates, and we establish novel results on their uniform convergence rates in high dimensions, involving responses indexed by a function class and usage of dimension reduction techniques. These results may be of independent interest. Numerical results on both simulated and real data confirm our semi-supervised approach's improved performance, in terms of both estimation and inference.

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