title: Quantifying App Store Dynamics: Longitudinal Tracking of Mental Health Apps.
abstract: BACKGROUND
  For many mental health conditions, mobile health apps offer the ability to deliver information, support, and intervention outside the clinical setting. However, there are difficulties with the use of a commercial app store to distribute health care resources, including turnover of apps, irrelevance of apps, and discordance with evidence-based practice.
  
  
  OBJECTIVE
  The primary aim of this study was to quantify the longevity and rate of turnover of mental health apps within the official Android and iOS app stores. The secondary aim was to quantify the proportion of apps that were clinically relevant and assess whether the longevity of these apps differed from clinically nonrelevant apps. The tertiary aim was to establish the proportion of clinically relevant apps that included claims of clinical effectiveness. We performed additional subgroup analyses using additional data from the app stores, including search result ranking, user ratings, and number of downloads.
  
  
  METHODS
  We searched iTunes (iOS) and the Google Play (Android) app stores each day over a 9-month period for apps related to depression, bipolar disorder, and suicide. We performed additional app-specific searches if an app no longer appeared within the main search
  
  
  RESULTS
  On the Android platform, 50% of the search results changed after 130 days (depression), 195 days (bipolar disorder), and 115 days (suicide). Search results were more stable on the iOS platform, with 50% of the search results remaining at the end of the study period. Approximately 75% of Android and 90% of iOS apps were still available to download at the end of the study. We identified only 35.3% (347/982) of apps as being clinically relevant for depression, of which 9 (2.6%) claimed clinical effectiveness. Only 3 included a full citation to a published study.
  
  
  CONCLUSIONS
  The mental health app environment is volatile, with a clinically relevant app for depression becoming unavailable to download every 2.9 days. This poses challenges for consumers and clinicians seeking relevant and long-term apps, as well as for researchers seeking to evaluate the evidence base for publicly available apps.
authors: Black Dog Institute, University of New South Wales, Sydney, Australia. mark.larsen@blackdog.org.au.
authors: Mark Erik
authors: http://orcid.org/0000-0002-0272-2053
authors: ME
authors: Larsen
authors: Jennifer
authors: http://orcid.org/0000-0003-1889-1107
authors: J
authors: Nicholas
authors: Helen
authors: http://orcid.org/0000-0003-0435-2065
authors: H
authors: Christensen
keywords: bipolar disorder; depression; mental health; mobile applications; mobile apps; suicide; telemedicine