Year	% of revenue
1990	19.657615112160567
1991	21.584158415841586
1992	22.987901104681747
1993	23.4375
1994	26.859504132231404
1995	24.299065420560748
1996	25.339981867633725
1997	24.28343949044586
1998	25.42727589815138
1999	24.876673713883015
2000	26.46113989637306
2001	24.396450498782745
2002	28.123169502104574
2003	23.860710268558485
2004	23.39517760218856
2005	25.685832608795135
2006	24.822222129262826
2007	22.34285406039917
2008	20.64539206619319
2009	20.30721620294084
2010	21.851208797635017
2011	22.939697043136693
2012	24.520427550695466
2013	22.80819220670032
2014	24.367452058608567
2015	23.718523124188504
2016	25.20297590166586
2017	24.690408807603593