Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.35853

Adequacy radii for stepped-wedge trials with time-varying effects

Stanisław M. S. Halkiewicz·Sergey Alexeev
View original source ↗Read source document ↗Export metadata ↓

Abstract

Complete stepped-wedge designs guarantee eventual intervention delivery, but their final periods contain no concurrent controls. Under exposure-time heterogeneity this creates a design-analysis tension: a constant-effect analysis can be precise while targeting a design-dependent contrast, whereas an exposure-time indicator (ETI) analysis targets a prespecified time-averaged effect but may be much less precise. We develop an adequacy radius that quantifies the size of exposure-time heterogeneity compatible with a prespecified tolerance for estimand mismatch, and combine it with precision calculations to compare complete wedges with rollout-constrained hybrid designs that retain a wait-list arm. For a balanced wedge with a wait-list under the Hussey-Hughes model, the wait-list share and the correlation act on the constant-effect GLS estimand through a single scalar; we prove that the radius increases strictly with the wait-list share and decreases strictly with the within-cluster correlation, but remains bounded. Numerical optimisation and a model-based redesign of a weekend allied-health trial show that intermediate hybrids make estimand-aligned ETI analysis materially more affordable, giving a robustness-precision frontier rather than a binary choice between a complete wedge and a parallel trial. A second trial, of digital adherence support for tuberculosis treatment, has the same radius but no detectable heterogeneity; its test of a constant effect would detect heterogeneity large enough to halve the coverage of the nominal interval only 37% of the time. The contribution is a diagnostic and design principle: when exposure-time heterogeneity is plausible, retaining concurrent controls reduces the price of analysing the estimand one intends to report.

Explore related subjects

stat.MEecon.EMstat.AP

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Stanisław M. S. Halkiewicz, Sergey Alexeev. 2026-10-26. Adequacy radii for stepped-wedge trials with time-varying effects. https://arxiv.org/abs/2610.35853

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Denoising Data with Measurement Error Using a Reproducing Kernel-Based Diffusion Model

Recent advancements in measurement technologies have facilitated the acquisition of high-resolution data in fields such as engineering, biology, and medicine. However, these observations are frequently corrupted by measurement noise. To address this challenge, we propose a denoising framework that employs diffusion models to recover the underlying error-free data distribution, thereby enabling reliable downstream analysis. Central to our framework is a novel Reproducing Kernel Hilbert Space (RKHS)-based method that trains the diffusion model using only error-contaminated data. This method admits a closed-form solution and achieves a fast convergence rate in terms of estimation error. Theoretically, we validate our approach by deriving an upper bound on the total variation distance between the distributions of the generated denoised data and the true error-free data. Extensive simulations demonstrate the superior empirical performance of our method compared to state-of-the-art baselines. Finally, we illustrate the framework's practical utility in digital health and epidemiology by applying it to Continuous Glucose Monitor (CGM) data and the association analysis between blood lipids and coronary heart disease.

stat.ME↗
arXiv2026

Two-stage least squares with treatment-covariate interactions for treatment effect heterogeneity

Treatment effect heterogeneity with respect to covariates is common in instrumental variable (IV) analyses. An intuitive approach, which we call the interacted two-stage least squares (2sls), is to regress the outcome on the treatment, covariates, and treatment-covariate interactions, using the IV, covariates, and IV-covariate interactions as instruments. We clarify the causal interpretation of the interacted 2sls under the local average treatment effect (LATE) framework when the IV is valid conditional on the covariates. Our main findings are twofold. First, we show that the coefficients on the treatment-covariate interactions from the interacted 2sls identify treatment effect heterogeneity with respect to covariates among compliers for any outcome-generating process if and only if the product of the IV propensity score and the covariates is linear in the covariates, a requirement we call the linear IV-covariate interactions condition. Second, when the covariate vector has dimension K and includes a constant term, we show that the linear IV-covariate interactions condition requires the IV propensity score to take at most K distinct values. The condition holds when (a) the covariates take exactly K distinct values, or (b) the IV is randomly assigned independently of the covariates, but is restrictive beyond these cases. These results underscore the difficulty of interpreting regression coefficients from specifications with treatment-covariate interactions when the covariates are not saturated and the IV is not unconditionally randomized, absent correct specification of the outcome model. We then connect these results to the literature on LATE estimation, and show that under the linear IV-covariate interactions condition, the interacted 2sls with covariates demeaned by their complier means recovers the LATE as a single coefficient.

stat.ME↗
arXiv2026

Sliding-Window Signatures as Features for Time Series Forecasting

The evolution of a time series is often influenced not only by its past values but also by external covariates, giving rise to forecasting with exogenous variables. Nonlinear and delayed effects between covariates and the target series make this task particularly challenging. We propose a forecasting framework based on Ridge regression with sliding-window signature features, combining the computational efficiency of (semi-)parametric models with the flexibility of nonparametric approaches. These features capture complex dependencies between the target and the exogenous variables without relying on prior assumptions about the form of these relationships or the influence of past observations. We establish theoretical guarantees in the discrete-time setting, including universality of approximation and stationarity for the sliding-window transform. To ease implementation, we introduce a novel sequential algorithm that exploits window overlap for efficient signature updates. The method is evaluated on both synthetic and real electricity demand data. Results show that signature features effectively encode temporal and nonlinear dependencies, yielding accurate forecasts competitive with those based on expert knowledge and recent neural network approaches.

stat.ME↗