Year	% of revenue
1974	7.6923076923076925
1975	7.142857142857142
1976	8.064516129032258
1977	7.777777777777778
1978	8.333333333333332
1979	7.213114754098362
1980	8.464849354375897
1981	9.49367088607595
1982	8.101730466701627
1983	7.2002165478661
1984	7.012121421417965
1985	6.496761166457428
1986	4.7839113792700605
1987	6.538739627230732
1988	5.874784967676021
1989	6.997301549368702
1990	7.645084751271676
1991	6.528042236454907
1992	5.943152454780361
1993	6.149722803539303
1994	6.2641212196588105
1995	9.74451788899381
1996	9.911589847092117
1997	12.440353376302324
1998	12.755929307428996
1999	13.080414416162661
2000	14.813055836449418
2001	15.764852170688053
2002	16.04249930505537
2003	16.748896034522065
2004	16.785812193984512
2005	16.585040262654456
2006	15.71282065764489
2007	15.66727471810528
2008	16.982287814771993
2009	17.84489702220506
2010	17.67786105730779
2011	17.718928774659712
2012	17.606481586163074
2013	17.260845072120958
2014	17.072464256838554
2015	17.04326469043427
2016	17.30664462238688
2017	16.856159074383793
2018	17.711858699959457
2019	17.959544583878493
2020	18.01225716510604
2021	16.2688803398099
2022	15.803732573037212