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	38.752637866891256
2002	38.78098880252257
2003	40.011004561019334
2004	40.52442049541775
2005	39.55860699022274
2006	40.46580801129168
2007	40.812053529554326
2008	43.145774492593226
2009	43.49811457029186
2010	37.404971602690225
2011	37.690088351434156
2012	37.982094999364485
2013	32.93661259996605
2014	34.12008194668958
2015	33.34627614255229
2016	31.945584318395042
2017	28.1292951883417
2018	27.454848576609482
2019	29.597930611123346
2020	33.23860639146392