Year	% of revenue
1975	3.1572164948453607
1976	4.100742767293205
1977	4.4928522804629
1978	4.955681991326555
1979	5.93231894499986
1980	6.970095828956527
1981	6.312513880574673
1984	8.39151708556458
1985	10.244815219086231
1986	10.653045234005363
1987	9.792662317602806
1988	9.738594752234349
1990	9.54081320168299
1991	7.4896358594686605
1992	7.6026394960962005
1993	7.593030051520102
1994	8.11035996556368
1995	7.709496043676562
1996	7.415342308061266
1997	8.975329524656546
1998	8.148767041021681
1999	7.591545971829085
2000	7.6540472649983675
2001	6.7045544175279534
2002	6.476647859942706
2003	5.9680277512865025
2004	4.970066421450516
2005	4.7917358571939
2006	4.389276695351052
2007	4.254415170257457
2008	3.9954998285328562
2009	4.757276977153751
2010	5.100043544446675
2011	5.500780604197642
2012	5.352352722782022
2013	5.171815350740829
2014	5.274039601746275
2015	5.005505436201039
2016	4.587208838241461
2017	4.090224293033143
2018	3.7447904885627494
2019	3.669571786165711
2020	3.5011060347987644
2021	3.0868886497453816
2022	3.1252453740603094