Year	% of revenue
1988	35.19935118827909
1989	33.252190446137234
1990	40.87122801235112
1991	34.990436712234754
1992	36.29940355574831
1993	35.54627977132404
1994	37.93512208376007
1995	35.741165720886194
1996	38.518546217876256
1997	39.76851496613764
1998	39.42002214159957
1999	36.2567873748128
2000	38.88044252514012
2001	37.191814568855044
2002	32.73807206814867
2003	40.54243085820555
2004	41.219852047349605
2005	45.59942045796514
2006	50.385243424121555
2007	49.055851316081814
2008	52.96980862328812
2009	45.48769607995072
2010	43.50115982309219
2011	50.99013465786313
2012	45.49302817564059
2013	40.79022287563278
2014	41.30198738303886
2015	34.994768735359926
2016	32.618703409987276
2017	25.306785958950726
2018	27.97696884251168
2019	27.844912150451442
2020	33.23860639146392