title: Analyzing mHealth Engagement: Joint Models for Intensively Collected User Engagement Data.
abstract: BACKGROUND
  Evaluating engagement with an intervention is a key component of understanding its efficacy. With an increasing interest in developing behavioral interventions in the mobile health (mHealth) space, appropriate methods for evaluating engagement in this context are necessary. Data collected to evaluate mHealth interventions are often collected much more frequently than those for clinic-based interventions. Additionally, missing data on engagement is closely linked to level of engagement resulting in the potential for informative missingness. Thus, models that can accommodate intensively collected data and can account for informative missingness are required for unbiased inference when analyzing engagement with an mHealth intervention.
  
  
  OBJECTIVE
  The objectives of this paper are to discuss the utility of the joint modeling approach in the analysis of longitudinal engagement data in mHealth research and to illustrate the application of this approach using data from an mHealth intervention designed to support illness management among people with schizophrenia.
  
  
  METHODS
  Engagement data from an evaluation of an mHealth intervention designed to support illness management among people with schizophrenia is analyzed. A joint model is applied to the longitudinal engagement outcome and time-to-dropout to allow unbiased inference on the engagement outcome. Results are compared to a naïve model that does not account for the relationship between dropout and engagement.
  
  
  RESULTS
  The joint model shows a strong relationship between engagement and reduced risk of dropout. Using the mHealth app 1 day more per week was associated with a 23% decreased risk of dropout (P<.001). The decline in engagement over time was steeper when the joint model was used in comparison with the naïve model.
  
  
  CONCLUSIONS
  Naïve longitudinal models that do not account for informative missingness in mHealth data may produce biased results. Joint models provide a way to model intensively collected engagement outcomes while simultaneously accounting for the relationship between engagement and missing data in mHealth intervention research.
authors.affiliation: Department of Biomedical Data Science, Dartmouth Geisel School of Medicine, Hanover, NH, United States.
authors.forename: Emily A
authors.identifier: http://orcid.org/0000-0002-6166-4455
authors.initials: EA
authors.lastname: Scherer
authors.affiliation: Department of Biomedical Data Science, Dartmouth Geisel School of Medicine, Hanover, NH, United States.
authors.forename: Dror
authors.identifier: http://orcid.org/0000-0001-6597-2407
authors.initials: D
authors.lastname: Ben-Zeev
authors.affiliation: Department of Biomedical Data Science, Dartmouth Geisel School of Medicine, Hanover, NH, United States.
authors.forename: Zhigang
authors.identifier: http://orcid.org/0000-0002-6224-1833
authors.initials: Z
authors.lastname: Li
authors.affiliation: Psychiatry, Neurology, and Neuroscience, Hofstra Northwell School of Medicine, Hepstead, NY, United States.|Department of Psychiatry, Zucker Hillside Hospital, Glen Oaks, NY, United States.
authors.forename: John M
authors.identifier: http://orcid.org/0000-0002-2628-9442
authors.initials: JM
authors.lastname: Kane
keywords: engagement; informative missingness; joint models