Year	% of revenue
1972	6.745900737317047
1973	6.934268909297287
1974	5.786338039663756
1975	5.633265513733469
1976	5.138696992241472
1977	6.409269904494637
1978	6.855821253045885
1979	7.505686125852919
1980	7.287303664921466
1981	7.134925041643532
1982	6.892350327297052
1983	7.363969305894663
1984	8.564451767882312
1985	9.572721888484644
1986	10.653045234005363
1987	10.62909619979444
1988	9.20361218330267
1989	8.201996683177558
1990	7.447712286095716
1991	6.159110350727117
1992	5.981082796582833
1993	5.53680291313776
1994	6.3958480045533035
1995	7.144983104854948
1996	7.415342308061266
1997	7.1430163695673174
1998	6.023120898927033
1999	7.561545602970836
2000	6.093106441483691
2001	3.334811992798058
2002	2.894219186019915
2003	2.3651951040414576
2004	1.8868006650591505
2005	1.712317821529021
2006	1.5510400830583262
2007	1.4367566478226275
2008	1.336669436141326
2009	1.545938679489168
2010	2.2997412626906053
2011	3.09609125060779
2012	3.686475072514773
2013	3.46491146553807
2014	3.509059646839053
2015	3.8509690773380165
2016	3.915626899981348
2017	3.8046166999145057
2018	3.7046149227093226
2019	3.4932510995399624
2020	3.4861351581608817
2021	3.2065611738579145
2022	3.0820464003396086