Year	% of revenue
1972	19.019607843137226
1973	19.20472304219479
1974	14.876152073732719
1975	14.667542994851562
1976	14.600604701063125
1977	19.26596758817924
1978	20.97712600621659
1980	27.005554383744613
1981	24.48637784725326
1982	24.911697485975594
1983	23.879463155229104
1984	22.33119966962619
1985	22.746890073622655
1986	23.19405658886142
1987	23.08466673731063
1988	20.250405948209576
1989	21.739858500439556
1990	20.31961090845925
1991	19.858401510383903
1992	23.70002273539252
1993	25.901903936396025
1994	24.98670770952843
1995	22.098281016442453
1996	19.066679135883287
1997	22.224579560155238
1998	21.738126475990555
1999	22.978280680437425
2000	24.341643059490085
2001	25.532355305466236
2002	26.967038444762913
2003	28.223090481786134
2004	26.21728843402663
2005	25.76976847950027
2006	27.571603947306293
2007	31.074175577320513
2008	30.67547686254384
2009	32.26435218629159
2010	30.192481085107215
2011	30.533220338983053
2012	31.93282943525385
2013	33.29332315656733
2014	32.2446047472238
2015	31.97916722813637
2016	34.096191768893895
2017	34.07395664687893
2018	33.241259674406194
2019	35.2688176273854
2020	34.940164563437925
2021	37.159200731356925
2022	37.733934669380155