Year	% of revenue
1999	16.31681272698563
2002	17.515656868790686
2003	18.866851221524875
2004	17.49522498586169
2005	16.757384819696966
2006	15.980974922037031
2007	16.38051649394466
2008	17.58449177497951
2009	18.146173718853333
2010	18.30101420289725
2011	17.209912564340833
2012	18.720684467529647
2013	19.73607299838448
2014	18.60699505362722
2015	20.14733108511879
2016	19.661285179155605
2017	19.384799362355835
2018	18.97646330997489
2019	19.08541618365707
2020	17.573041231350608
2021	17.843948562144654