Year	% of revenue
1990	31.634697436277964
1991	29.12632775447811
1992	25.98991711526959
1993	21.44309100783614
1994	21.030990304709142
1995	22.73655739783341
1996	21.335268505079828
2004	18.331475373313914
2005	17.967038357149864
2006	15.927931875433753
2007	18.28203190930817
2008	17.56623089079512
2009	18.352781398290556
2010	19.48486066140222
2011	17.551376744083118
2012	19.254906178361352
2013	20.497569403885656
2014	20.566357588042333
2015	19.776153532411566
2016	20.252726010123702
2017	18.70368226786582
2018	19.090288636543974
2019	19.365354242432726
2020	20.53152092195193
2021	13.421844735415785