The "formula" (see below) was inspired by a recent #mHealthPharma Tweet Chat that I moderated on October 9, 2014, at the request of the Mobile Health Competence Centre in Barcelona (find a StoryLine summary here).
So what is the "formula?"
This formula is actually a rephrasing of the one presented by @estherdelcampo (Esther del Campo, a journalist in Barcelona & a "social media ninja"). Esther posted this version of the formula:
satisfying patients'needs + transparency + reliability in managing the health data = a quality mHealth app
"Health Data Security" was my interpretation of Esther's "reliability in managing the health data," which probably is more patient-friendly. But you get the idea: it's about privacy and data security, two topics I have written about often (see, for example, "Many Smartphone Apps Lack Privacy Policies").
After the presentation, David L. Scher, MD, noted that "Efficacy" was missing from my original formula. I added that within "Satisfy Patients' Needs" in the updated version as shown above.