The widespread availability of smartphones, tablets, and smartwatches has led to exponential growth in the number of mobile health (mHealth) studies conducted. Although promising, the key challenge of all apps (both for research and nonresearch) is the high attrition rate of participants and users. Numerous factors have been identified as potentially influencing engagement, and it is important that researchers consider these and how best to overcome them within their studies. This article discusses lessons learned from attempting to maximize engagement in 2 successful UK mHealth studies-Cloudy with a Chance of Pain and Quality of Life, Sleep and Rheumatoid Arthritis.
