An Empirical approach to Survival Density Estimation for randomly-censored data using Wavelets

TL;DR

This paper introduces a wavelet-based non-parametric density estimator for right-censored survival data, demonstrating its asymptotic properties and robustness through simulations and real data applications.

Contribution

It develops a fully data-driven wavelet estimator for censored data, with proven asymptotic unbiasedness, normality, and mean square consistency, advancing survival density estimation methods.

Findings

Estimator is asymptotically normal

Provides global mean square consistency

Performs well in simulations and real data applications

Abstract

Density estimation is a classical problem in statistics and has received considerable attention when both the data has been fully observed and in the case of partially observed (censored) samples. In survival analysis or clinical trials, a typical problem encountered in the data collection stage is that the samples may be censored from the right. The variable of interest could be observed partially due to the presence of a set of events that occur at random and potentially censor the data. Consequently, developing a methodology that enables robust estimation of the lifetimes in such setting is of high interest for researchers. In this paper, we propose a non-parametric linear density estimator using empirical wavelet coefficients that are fully data driven. We derive an asymptotically unbiased estimator constructed from the complete sample based on an inductive bias correction procedure. Also, we provide upper bounds for the bias and analyze the large sample behavior of the expected $\mathbb{L}_{2}$ estimation error based on the approach used by Stute (1995), showing that the estimates are asymptotically normal and possess global mean square consistency. In addition, we evaluate the proposed approach via a theoretical simulation study using different exemplary baseline distributions with different sample sizes. In this study, we choose a censoring scheme that produces a censoring proportion of 40\% on average. Finally, we apply the proposed estimator to real data-sets previously published, showing that the proposed wavelet estimator provides a robust and useful tool for the non-parametric estimation of the survival time density function.