Year	% of revenue
1972	23.60091635887606
1973	24.977453472165287
1974	26.197680282400405
1975	28.107533518499466
1976	28.274287918729506
1977	27.876976111604858
1978	28.261756727560794
1979	27.71888174859809
1980	28.22415182824064
1981	27.99512339986558
1982	29.852488591743604
1983	31.31237372191269
1984	32.68598953112819
1985	32.90416324467749
1986	33.915705833039716
1987	32.81857949924161
1988	34.233354457338166
1989	33.90760116573504
1990	35.333075420949854
1991	34.53134431318444
1992	36.20937316119207
1993	34.99042586712558
1994	35.0693374422188
1995	34.14530450661425
1996	33.667313712803015
1997	32.74208753400064
1998	32.16066420335663
1999	32.427240519616845
2000	31.257407811270305
2001	35.025459078932634
2002	38.90803968991015
2003	39.696906435615396
2004	39.30244550177852
2005	36.4943757453438
2006	35.17573243354375
2007	35.0658229372815
2008	37.2324632283916
2009	41.894472411414
2010	39.31789156159824
2011	34.80451299630879
2012	34.444981706821984
2013	34.500561568703986
2014	34.320282862554016
2015	34.25832864172633
2016	35.10934497277161
2017	34.083021957140126
2018	37.28826667722598
2019	37.82596284886643
2020	37.848058735837135
2021	34.86724845636319
2022	33.44644875915079