Year	% of revenue
1972	24.449182658137865
1973	23.096942094990244
1974	23.413581964931804
1975	23.590686274509906
1976	23.742328727090563
1977	25.694664553618612
1978	25.74941250644802
1979	26.820649630253623
1980	25.820960948369564
1981	29.85469616018368
1982	33.15703124103674
1983	30.91898417915208
1984	32.99122807017533
1985	33.993987104875536
1986	30.71735423830525
1987	28.79495905042572
1988	28.995950008696315
1989	30.630932140992517
1990	27.436904496555453
1995	30.500158277936055
1996	29.564977213092114
1997	28.131526430593585
1998	27.918123842830695
1999	28.327422601361068
2000	28.233484819685163
2001	29.742695159180116
2002	32.654879931252886
2003	33.299487838019445
2004	32.2922837422679
2005	32.41218974148977
2006	31.421497833711577
2007	31.882234802087815
2008	32.36919111355257
2009	33.09834530832309
2010	33.210332103321036
2011	31.191527323466843
2012	30.720673936876118
2013	28.55058081839939
2014	29.91814986399712
2015	29.78401648840811
2016	29.49856699590232
2017	31.04831967898345
2018	30.745465184318316
2019	31.05115390440243
2020	32.073735043058335
2021	31.023774314639972
2022	29.027647282250165