Year	% of revenue
1972	8.920863309352525
1973	9.619952494061792
1974	11.506276150627592
1975	13.647642679900752
1976	13.198281154082236
1977	13.243662700465567
1978	12.898936170212789
1979	12.903225806451605
1980	12.788732394366201
1981	12.694827196747227
1982	13.144283930800787
1983	12.952731737262127
1984	13.00779076238169
1985	13.006646683174738
1986	13.099723687515791
1987	12.81783350748876
1988	13.311723392760626
1989	13.99978478424623
1990	14.083808579221465
1991	14.062370750268894
1992	14.25623387790194
1993	14.35339279018647
1994	13.983486274621884
1995	15.434386953575272
1996	14.387480003266006
1997	13.751403644796431
1998	13.295939878592991
1999	13.09156082211903
2000	13.313000213549802
2001	14.440205982184901
2002	14.76088670389633
2003	14.608453818889647
2004	14.558431955686968
2005	15.270274578489229
2006	14.684059536849107
2007	15.676720579549297
2008	17.588186298699878
2009	18.959347284688956
2010	17.776964845223837
2011	19.407118972389632
2012	18.380525006259578
2013	18.105413972646172
2014	17.885681946659954
2015	17.407849798385726
2016	17.92893385516657
2017	18.177432021031613
2018	18.08523219188043
2019	18.427041028957483
2020	18.626758288624774
2021	17.541997436946474
2022	17.457229751451692