This dataset provides the proportion of developers, by market share, that have certified 2015 edition health IT modules. Market share approximations are determined through an analysis of the certified health IT products reported by participants in the Medicare EHR Incentive Program from 2011 to 2016. Approximations use the most recently reported data for each unique clinician and hospital participant. It is important to understand how to interpret these approximations. Some clinicians and hospitals report certified software from more than one unique developer. The market share percentages in this dataset, therefore, include some double counting (the percentages will, if summed together, add up above 100 percent.) The approximations convey the percent of hospitals and clinicians who use a developer's technology, and are not to be interpreted in aggregate as the percent of all hospitals and clinicians who have access to 2015 edition certified technology.