Year	% of revenue
1972	45.13983165897366
1973	45.36914277055949
1974	45.50433954276038
1975	44.200344712268155
1976	46.93766937669377
1977	47.62169413568417
1978	45.95042888962608
1979	46.405603145259974
1980	46.26206327088816
1981	45.215711964335846
1982	47.62723919479961
1983	50.190881475602744
1984	46.20031634915291
1985	45.616926903827135
1986	47.99379070630716
1987	49.47247087676272
1988	47.293032006281535
1989	46.79141326226158
1990	43.34978364875941
1991	44.79066583645008
1992	42.91519961807006
1993	41.15140565403716
1994	40.5463352419606
1995	40.595455172308114
1996	41.67397240258258
1997	42.63190742575107
1998	47.856607122106844
1999	44.77513093973744
2000	42.05070409679366
2001	38.73641956232398
2002	42.27192832166607
2003	40.04958904841552
2004	40.09080760150899
2005	40.12462982411542
2006	39.93623310649146
2007	39.75595050159286
2008	36.860236220472444
2009	38.253755123840264
2010	40.22312793840781
2011	39.45119394217428
2012	39.09989590979056
2013	42.34230518727062
2014	41.71671983861117
2015	42.656235350016765
2016	42.555739177567546
2017	43.393134664977225
2018	42.3015052747776
2019	40.73018261642004
2020	41.2474797086991
2021	42.86173486330296
2022	41.43337543627293