Year	% of revenue
1972	28.202616665500614
1973	29.761904761904805
1974	28.325682022056874
1975	27.261667234415278
1976	28.05469783855316
1977	27.244825686629337
1978	25.912899555187714
1979	26.066842900302117
1980	25.479854746671254
1981	25.369973330544404
1982	25.469728601252612
1983	26.237908246336595
1984	27.11337724577099
1985	26.91968411324874
1986	26.73434516031762
1987	26.85968819599116
1988	25.91415800527755
1989	26.125477696090986
1990	25.53116992663079
1991	24.834295959907628
1992	24.552975713904466
1993	23.968583435834528
1994	25.240393426599116
1995	27.06049846996748
1996	27.449691088778806
1997	27.85810712465908
1998	27.84201554584832
1999	28.030370879093674
2000	28.004541852586566
2001	27.17599485248583
2002	28.08668613867546
2003	28.008756436175968
2004	28.032550788082055
2005	27.665154537537113
2006	27.122154264121324
2007	26.76932140209034
2008	26.41486132164318
2009	27.018407157772145
2010	27.21378719075233
2011	27.340358305822253
2012	27.360819603510745
2013	26.73429515885022
2014	26.590636494856206
2015	26.349020950386315
2016	26.98409367086479
2017	27.160635272953442
2018	26.630108652705974
2019	26.463829642367227
2020	26.147175798196038
2021	25.824317769193954
2022	25.853362964996318