 A 2016 study conducted by researchers from the University of California, Davis found that the federal tax credit was the reason behind more than 30% of the plug-in electric sales.The impact of the federal tax incentive is higher among owners of the Nissan Leaf, with up to 49% of sales attributable to the federal incentive.The study, based on an stated preference survey of more than 2,882 plug in vehicle owners in 11 states, also found that the federal tax credit shifts buyers from internal combustion engine vehicles to plug-in vehicles and advances the purchase timing of new vehicles by a year or more.