Larsen ME, Nicholas J, Christensen H. (2016). Quantifying app store dynamics: Longitudinal tracking of mental health apps. JMIR Mhealth and Uhealth. 4(3). PMCID: PMC4995352
This study examined the mobile applications (apps) for mental health available in iTunes and Google Play app stores. Researchers tracked results of daily searches for depression, bipolar disorder, and suicide daily over nine months. Researchers calculated “result half-life”, or how long it took for half the apps appearing in the initial search to no longer appear in searches, and “app half-live”, or how long it took for half the apps identified in the initial search to no longer be available. These constructs delineated the difference between app visibility and app availability. The searches for depression, bipolar disorder, and suicide had result half-lives of 130, 195, and 115 days respectively on Google Play. In the iTunes store, more than half the results remained at study end, thus did not reach their result half-life. More than half of the apps in the initial search were still available in both stores by study end, thus did not reach their app half-lives. About 30-40% of apps were clinically relevant and less than 10 provided evidence of effectiveness and six referenced specific studies. This study demonstrated the difficulties that consumers have searching for quality mental health apps and suggested that Google Play is a more volatile marketplace than iTunes. Additionally, the differences between app visibility and availability can be a concern to researchers and developers who create apps that, even the app is still available, are not reaching target audiences because of low visibility.