Year	% of revenue
1972	38.825644098262444
1973	37.889514615178335
1974	35.60655737704923
1975	34.48876839659169
1976	34.0076457470532
1977	32.0457796852646
1978	32.84165405950577
1979	33.075045111983954
1980	31.48625811616127
1981	30.519530946649127
1982	30.66844919786096
1983	30.08489776396025
1984	29.413687881429762
1985	29.781752046074573
1986	29.573040125660395
1987	29.680076121057663
1988	29.564016030373153
1989	28.99809908518468
1990	28.39991770470942
1991	26.945171936548505
1992	26.791578801811443
1993	26.73626561697777
1994	27.731424990930865
1995	26.340105203078963
1996	26.624612729408014
1997	26.615104963627523
1998	26.59102476441163
1999	26.382971766744596
2000	25.823891958334187
2001	24.98011341766955
2002	25.387570964221247
2003	25.46505391313523
2004	24.99712226580157
2005	24.533191815238276
2006	24.052983805415664
2007	23.48658007808668
2008	22.723934774444633
2009	22.77667787075732
2010	22.120329033249355
2011	22.346773292215893
2012	22.090665395203963
2013	21.872499163066525
2014	21.98527969006358
2015	22.276840278134404
2016	22.46098627033414
2017	22.692903592380016
2018	22.900794007376067
2019	23.459617321822414
2020	23.18864421470675
2021	20.788248627004457
2022	20.185216610439575