Due to changes in tax rules , the plug - in market share declined from 9.9 % in 2015 , to 6.7 % in 2016 .
Due to changes in tax rules , the plug - in market share fell to 2.6 % in 2017 .
Due to changes in tax rules , the plug - in market share declined from 9.9 % in 2015 , to 6.7 % in 2016 , and fell to 2.6 % in 2017 .