Year	% of revenue
1972	32.91139240506329
1973	32.715008431703204
1974	31.564245810055862
1975	30.14705882352941
1976	30.89770354906054
1977	27.12680577849117
1978	21.894303363074812
1979	20.57580028186028
1980	20.93515286152544
1981	20.872878420505717
1983	23.31365569927945
1984	23.455879641579706
1985	27.32289181620164
1986	30.984008437615802
1987	33.15714987147272
1988	31.955185915573463
1989	29.432126305263363
1990	31.191715090525797
1991	31.603560084029347
1992	33.530211488884
1993	32.27432089455646
1994	36.37283723224711
1995	39.37124636422339
1996	46.31118997203798
1997	45.248366969092416
1998	39.596129435862245
2008	35.368769845664985
2009	35.42600850951984
2010	38.85515046953885
2011	39.188661329002706
2012	37.51673003108375
2013	40.808990915714276
2014	38.31755898616665
2015	39.64044401485693
2016	38.53404490149007
2017	38.49343616553054
2018	34.141158224490084
2019	33.51454017340318
2020	37.26975422813289
2021	35.23192795308174
2022	37.71284633963277