Mark Benden

Wearable devices collect time-varying biobehavioral data, offering opportunities to investigate how behaviors influence health outcomes. However, these data often contain measurement error and excess zeros (due to nonwear, sedentary behavior, or connectivity issues), each characterized by subject-specific distributions. Current statistical methods fail to address these issues simultaneously. We introduce a novel modeling framework for zero-inflated and error-prone functional data by incorporating a subject-specific time-varying validity indicator that explicitly distinguishes structural zeros from intrinsic values. We iteratively estimate the latent functional covariates and zero-inflation probabilities via maximum likelihood, using basis expansions and linear mixed models to adjust for measurement error. To assess the effects of the recovered latent covariates, we apply joint quantile regression across multiple quantile levels. Through extensive simulations, we demonstrate that our approach significantly improves estimation accuracy over methods that only address measurement error, and joint estimation yields substantial improvements compared with fitting separate quantile regressions. Applied to a childhood obesity study, our approach effectively corrects for zero inflation and measurement error in step counts, yielding results that closely align with energy expenditure and supporting their use as a proxy for physical activity.

Read full publication

This study investigates the effect of air gaps between 10-layer Kevlar® soft body armor and the female torso on armor performance using an anatomically accurate manikin constructed of Roma Plastilina No.1 clay as the backface witness material. The clay torso was outfitted with silicone breasts and sports bras in B and F cup sizes to simulate realistic armor wear conditions. Ballistic testing employed an HG2-level threat against the armor at three sites: the xiphoid process, the inframammary region, and a control location with full armor contact. Pre- and post-donning 3D scans quantified the air gaps. Results showed that air gaps at the xiphoid process significantly reduced clay deformation, suggesting a protective effect on the body simulant correlated with increased gap depths at that location. Although 22 of 24 under-breast shots showed significantly less deformation than a control shot, one shot in each bra size perforated the armor and penetrated the manikin, a catastrophic failure. This study introduces a novel and functionally realistic testing approach for armor and challenges previous assumptions on air gaps while highlighting the need for additional testing.

Read full publication

Reducing sedentary behavior in youth is a global health priority, with classroom-based interventions, such as standing desks, offering potential benefits. This study used community-engaged research (CEnR) methods to inform the development of a standing desk intervention by assessing teacher perspectives on implementation barriers and relevant study outcomes in K-12 schools.

Read full publication