Year	% of revenue
1998	7.995966725485254
1999	8.089922194544393
2000	5.567471198834379
2001	5.728805728805729
2002	6.716709333101923
2003	7.7870978900034595
2004	6.994184880689794
2005	6.561717871522362
2006	5.973676338618008
2007	5.16642583719928
2008	4.033294985450362
2009	4.940023562172004
2010	4.7707226743336095
2011	4.399771436881252
2012	4.371998801063361
2013	4.55758812907278
2014	3.917940588176838
2015	3.594305039776878
2016	3.539556499752249
2017	3.3205292221291045
2018	3.4383694205878794
2019	3.4758517409210037
2020	2.994021573624401
2021	3.384039697388758