Year	% of revenue
1972	27.55632582322357
1973	25.77777777777778
1974	26.900584795321635
1975	22.164948453608247
1976	26.01555747623163
1977	25.051055139550716
1978	25.538687561214495
1979	25.688244047619047
1980	22.32116355001484
1981	22.94352003749707
1982	23.868354430379746
1983	22.849886144683833
1984	22.9158340660219
1985	25.287523657009753
1986	25.24648559251956
1987	28.606158833063212
1988	30.339569110736768
1989	34.758058191514394
1990	33.968466743265665
1991	31.253477244909313
1992	32.822486587357126
1993	31.398872233259084
1994	31.229803264964417
1995	31.48231774434817
1996	29.090887177447545
1997	26.770994048931012
1998	29.339355756271758
1999	23.791075407629144
2000	26.281535561230484
2001	25.121281602897998
2002	24.705702746507175
2003	27.595413679107168
2004	27.45354790617646
2005	28.88244416676037
2006	29.29215340137672
2007	31.47090946059114
2008	30.6192250678245
2009	28.38339889251434
2010	28.11729632255391
2011	30.32686893355796
2012	24.491952089029446
2013	24.041483391862347
2014	24.91548373747232
2015	26.198937096728176
2016	27.20663069756525
2017	28.340191337644022
2018	30.42204934201879
2019	29.375305182623002
2020	28.05509938834868
2021	30.40023633388727
2022	33.88033562667927