Year	% of revenue
1972	5.769230769230769
1973	13.461538461538462
1974	8.955223880597014
1975	12.359550561797752
1976	9.649122807017543
1977	15.09433962264151
1978	27.376425855513308
1979	25.045372050816695
1980	21.00098135426889
1981	25.08207485226527
1982	22.414486921529175
1983	37.74745853397539
1984	32.489009838810965
1985	30.86578693273254
1986	22.272133831957692
1987	23.900999638684812
1988	32.50620347394541
1989	28.47046272836378
1990	61.61112414926073
1991	28.03083391730904
1992	29.249354406141485
1993	27.5367338321322
1994	21.77944603683039
1995	19.236246386268057
1996	13.737410000199446
1997	10.442949498993846
1998	11.292414584229531
1999	13.039471511147813
2000	13.500855182898794
2001	12.787051917994638
2002	12.569236148169956
2003	12.410013455931823
2004	11.949083188280214
2005	10.563617081813714
2006	9.466784964406386
2007	8.741263956389423
2008	7.633663770417525
2009	6.999923092784062
2010	5.828189707518565
2011	5.4498148306453
2012	4.948068349212147
2013	5.045083596334841
2014	4.816217305901063
2015	5.106365175654278
2016	5.742680484221215
2017	6.210339638332352
2018	6.460655985547745
2019	6.425923150325094
2020	8.164454224114188
2021	6.5542006492536276