Year	% of revenue
1973	30.6622023809524
1974	28.325682022056874
1975	28.1086729362592
1976	28.05469783855316
1977	27.570697278918846
1978	25.777125765303172
1979	26.13698765977081
1980	27.41030158953597
1981	27.862516914749662
1982	28.578609794922876
1983	29.531160411061613
1984	28.903996115329846
1985	29.781752046074573
1986	29.573040125660395
1987	29.665236199612618
1988	30.263586003898038
1990	30.60000999184
1991	28.111419693599363
1992	27.405032067094176
1993	29.512989648292937
1994	30.974783999336832
1995	30.398641114415657
1996	30.36439023320097
1997	29.68533857905557
1998	30.85239210488663
1999	32.5274959350748
2000	31.660140399724014
2001	31.691619345618662
2002	32.21930257259553
2003	32.57948641617712
2004	32.34033106365702
2005	32.04937330359283
2006	32.16889821774314
2007	32.23017224190555
2008	30.984313675590247
2009	30.822157302863847
2010	30.63865955175733
2011	30.963453431372674
2012	30.89468130486518
2013	30.563306286848402
2014	30.84132019083205
2015	30.722977783450514
2016	30.126806942932667
2017	30.988090761161992
2018	29.382778327094307
2019	28.75986647479783
2020	29.380556745192262
2021	30.44141163058312
2022	28.457801356855434