Year	% of revenue
1972	21.46833157815556
1973	22.056737588652485
1974	23.638660770688567
1975	26.707212974818606
1976	26.611328125
1977	27.88236129857214
1978	31.044293566117037
1979	32.53286906405715
1980	33.01204819277108
1981	34.982216398352676
1982	35.44912164401723
1983	34.093831514750725
1984	33.30857899325175
1985	27.798555400119906
1986	29.809501099541635
1987	28.51026032295534
1988	29.13235294117647
1989	30.470658997782042
1990	31.407683724957952
1991	31.302638046862196
1992	37.32243212688218
1993	34.788580762519956
1994	33.81578947368421
1995	15.056163919620683
1996	15.972768126634918
1997	16.784525495065157
1998	11.904937660568056
1999	11.440709400718674
2000	13.05587808338731
2001	12.747164758410726
2002	11.34429752352564
2003	11.120890167177576
2004	10.783271626636246
2005	9.300612733904803
2006	8.464165848238919
2007	8.382734681557501
2008	8.845942789120679
2009	9.094660196333182
2010	8.761968502290172
2011	9.22110873781319
2012	9.49531995171536
2013	9.497106660863393
2014	9.468758151613192
2015	9.209841308541229
2016	9.013337696089344
2017	9.072134172468857
2018	9.200401285944668
2019	9.32603618805451
2020	9.61960945101615
2021	9.298832825563764
2022	8.932649657732247