A Modified Instrumental Variable Framework for Sensitivity-Based Estimation of Engagement in mHealth

Thomas M. Menino Convention & Exhibition Center 

Engagement with mobile health interventions has attracted growing attention, with identifying thresholds for effective engagement as a primary focus. However, in these settings, the exclusion restriction assumption is often unreasonable. Previous methodological advances have addressed this challenge by modifying instrumental variable (IV) approaches with sensitivity analyses to assess how engagement influences outcomes when the exclusion restriction may fail, but these methods have largely been limited to two treatment arms and continuous engagement measures.

We propose a modified instrumental variable (MIV) approach that extends prior work and broadens its application to real-world interventions. Our method accommodates multiple treatment groups and alternative engagement distributions, thereby expanding the range of settings in which engagement effects can be assessed. Under correct specification of a sensitivity parameter, the class of local average treatment effects (LATEs) is identifiable. Estimation proceeds via two-stage least squares to recover a weighted average of LATEs, and simulations demonstrate accurate recovery across diverse treatment and engagement settings.

Instrumental Variables

Sensitivity Analysis

Local Average Treatment Effecs

Multivalued Treatments

Mobile Health 

Section on Statistics in Epidemiology