Year	% of revenue
2006	18.63067623731496
2007	16.967055426091587
2008	18.744210678861915
2009	20.503693258898497
2010	20.447247510880835
2011	21.81936746005869
2012	21.314344550538227
2013	21.90259630069574
2014	21.512131090864077
2015	23.424202091476662
2016	22.429646207724335
2017	23.152142618651574
2018	24.273071498982127
2019	23.650320277643896
2020	24.964373980067442
2021	25.10223592231599