Year	% of revenue
1972	20.69126576366184
1973	19.192688499619194
1974	17.33418776033323
1975	20.165903890160184
1976	18.751461304652793
1977	17.941747572815533
1978	19.31657223796034
1979	18.569544188773268
1980	18.47287511116758
1981	19.093054273109676
1982	19.68047126026419
1983	21.022969857399026
1984	20.515817929422077
1985	17.63661121307205
1986	19.40818102697998
1987	24.847641261003687
1988	26.30545158062484
2001	28.935174350573366
2002	29.221401500052522
2003	28.969713189325287
2004	29.085800545560552
2005	27.25529475159568
2006	26.399974909438757
2007	25.88560409359389
2008	23.957578595317724
2009	24.527555392747118
2010	26.632876019991553
2011	27.495593521896293
2012	29.162332496246947
2013	28.92545606050218
2014	28.852727569754194
2015	29.031832143303564
2016	29.16364593286361
2017	29.10827540668759
2018	29.382778327094307
2019	28.75986647479783
2020	29.49092228858494
2021	30.297123531491295
2022	27.866955102733904