Year	% of revenue
1972	7.143858992940297
1973	6.579486759039107
1974	5.99020243498307
1975	5.626993107704969
1976	5.410531730212821
1977	4.678031833239073
1978	4.35701082651175
1979	3.7943596250665137
1980	4.411225910456511
1981	6.358336329107988
1982	5.478995163808918
1983	5.384803771505541
1984	5.157868359505513
1985	4.506917682734222
1986	3.947416380137777
1987	3.5182783407707015
1988	3.6381769637532853
1989	3.2086379054990206
1990	3.2128514056224895
1991	3.609554195050444
1992	3.8982728185248
1993	3.840156417900801
1994	4.106129505054681
1995	3.9671587281673846
1996	3.4933955543355357
1997	3.36613806810335
1998	3.1401638249565953
1999	3.61737304815641
2000	3.1826327716829597
2001	3.1306744418586545
2002	3.5194957469646417
2003	3.5755539668665772
2004	3.4970129362345155
2005	3.1677776878315544
2006	2.8181770762998433
2007	2.436888074373095
2008	2.4736833136708154
2009	3.010019280932959
2010	2.760906044379229
2011	2.956822575617042
2012	2.9988788733339864
2013	2.8443228914818963
2014	2.9900675872247042
2015	2.9846014309034534
2016	2.859872105002234
2017	2.4659418148936236
2018	3.05067333601562
2019	2.607930934294041
2020	2.287992868160566
2021	2.0254313988518233
2022	1.8233421114307369