Year	% of revenue
1972	23.380642879250104
1973	22.8725144498164
1974	19.60047756326253
1975	21.523977487875058
1976	20.3275465290345
1977	18.997288363715484
1978	18.700678696759784
1979	19.202655521730794
1980	20.625876181431803
1981	21.198341951672614
1982	22.16649067229854
1983	24.286489539609956
1984	25.513732209022656
1985	22.68848404128809
1986	25.437126621011185
1987	26.380906418637316
1988	27.210698689956352
1989	26.283456054230914
1990	24.66625604220501
1991	25.34636834377622
1992	27.17230704284817
1993	27.7065706481743
1994	27.399819581373734
1995	27.858628092155453
1996	27.772642998667475
1997	28.748882535267867
1998	29.61043348198446
1999	31.283781084511688
2000	32.315097385066274
2001	30.763296343872582
2002	30.021896606971264
2003	30.155401682548078
2004	32.6242686712593
2005	32.37689926534358
2006	31.701153195616243
2007	32.51154077832077
2008	30.3212034408207
2009	29.500359955454307
2010	29.741504019945715
2011	30.17376287487038
2012	30.483092925274203
2013	30.48497632312876
2014	31.5860400286749
2015	26.742141101607857
2016	26.95286179522906
2017	27.638332121601632
2018	26.797982242908574
2019	26.650396518380752
2020	26.542893199715635
2021	27.68552460171021
2022	27.061353890942268