RMME/STAT Joint Colloquium

Bayesian Longitudinal (Non)Linear Mediation Models

Dr. Nidhi Kohli

University of Minnesota, Twin Cities

Friday, May 2, at 11 AM ET

https://tinyurl.com/rmme-Kohli

This study develops Bayesian (non)linear random effects mediation models (B(N)REMM) to directly estimate both linear and nonlinear longitudinal mediation effects, overcoming limitations in existing structural equation modeling (SEM) approaches. We propose two models: a linear trend model (L-BREMM) and a segmented trend model using linear-linear piecewise functions with random changepoints (P-BREMM). We also examine the impact of omitting confounders in (non)linear mediation models using data from the Early Childhood Longitudinal Study-Kindergarten Cohort (ECLS-K). Furthermore, we extend this framework to develop Bayesian (nonlinear) growth mixture mediation models (B(N)GMMM), which assess heterogeneous treatment effects (HTE) of the intervention variable X on the longitudinal dependent variable Y, mediated by longitudinal variable M. To evaluate the robustness of these methods, we conducted a comprehensive Monte Carlo simulation study for all the models.

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RMME/STAT Joint Colloquium

Adventitious Error Everywhere

Dr. Paul De Boeck

The Ohio State University

Friday, February 7, at 11 AM ET

https://tinyurl.com/rmme-PDeBoeck

Adventitious error is a concept introduced by Wu and Browne (Psychometrika, 2015) to explain imperfect goodness of fit of covariance structure models (CSMs, i.e., factor models, SEM). The paper was published together with critical remarks from the reviewers. In my presentation I will discuss, illustrate, and speculate about the potential of adventitious error beyond CSM, (a) as a unitary framework to understand and deal with underestimated inferential uncertainty regarding relations between variables, heterogeneity in meta-analysis, violations of measurement invariance, individual differences in the validity of tests, and (b) as a joint framework for reliability and validity. The presentation is partly based on De Boeck, DeKay, and Pek (Psychometrika, 2024, 89, 1055-1073).

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RMME/STAT Joint Colloquium

Challenges in Time-varying Causal Effect Moderation Analysis in Mobile Health

Dr. Walter Dempsey

University of Michigan

Friday, January 24, at 11 AM ET

https://tinyurl.com/rmme-Dempsey

Twin revolutions in wearable technologies and smartphone-delivered digital health interventions have significantly expanded the accessibility and uptake of mobile health (mHealth) interventions in multiple domains of health sciences. Sequentially randomized experiments called micro-randomized trials (MRTs) have grown in popularity as a means to empirically evaluate the effectiveness of mHealth intervention components. MRTs have motivated a new class of causal estimands, termed “causal excursion effects”, that allow health scientists to answer important scientific questions about how intervention effectiveness may change over time or be moderated by individual characteristics, time-varying context, or past responses. In this talk, we present two new tools for causal effect moderation analysis. First, we consider a meta-learner perspective, where any supervised learning algorithm can be used to assist in the estimation of the causal excursion effect. We will present theoretical results and accompanying simulation experiments to demonstrate relative efficiency gains. Practical utility of the proposed methods is demonstrated by analyzing data from a multi-institution cohort of first year medical residents in the United States. Second, we will consider effect moderation with tens or hundreds of potential moderators. In this setting, it becomes necessary to use the observed data to select a simpler model for effect moderation and then make valid statistical inference. We propose a two-stage procedure to solve this problem that leverages recent advances in post-selective inference using randomization. We will discuss asymptotic validity of the conditional selective inference procedure and the importance of randomization. Simulation studies verify the asymptotic results. We end with an analysis of an MRT for promoting physical activity in cardiac rehabilitation to demonstrate the utility of the method.

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