Year	% of revenue
1990	27.302746877424088
1991	30.127935401344608
1992	32.676070579907986
2001	29.07394940068778
2002	29.689988248063067
2003	32.25469305489818
2004	33.71347002447355
2005	34.53605916921467
2006	34.101109247244324
2007	33.6809862858088
2008	31.512899153055052
2009	30.524037543842958
2010	30.632618029201776
2011	33.40211975572065
2012	32.33321873271648
2013	33.17102858619191
2014	33.414754819145614
2015	34.627928104670765
2016	32.96359493691682
2017	33.61884161799302
2018	33.868662013974955
2019	32.90457883012165
2020	33.29818507733019
2021	34.24651398601222