In March 2015, Apple promised to change the way medical research could be done. It launched ResearchKit, which could turn millions of iPhones around the world into a “powerful tool for medical research,” the company said at the time.

Since then, ResearchKit — software that gives would-be app developers a library of coding to create health apps on the iPhone and Apple Watch — has spawned a number of studies: One team has used it to create an app to track Parkinson’s symptoms; another is trying out a screening protocol for autism. A third helps people inventory the moles on their skin and evaluate how they have changed over time.