Year	% of revenue
1973	2.8490028490028525
1974	2.7310221825883367
1975	2.6706517547242474
1976	2.945853209473598
1977	3.0298473798962475
1978	3.249599888664672
1979	3.4728060531591587
1980	4.001888797072364
1981	4.89000278473963
1982	6.143722032113712
1983	7.131844631222957
1984	8.218582403246849
1985	8.907663345424503
1986	9.395373760828765
1987	9.457123864391738
1988	9.422268452303536
1989	9.342350544067312
1990	9.350948676791418
1991	9.182543198936695
1992	9.534217126477952
1993	9.784587899817927
1994	9.934385892966992
1995	11.115304338449926
1996	10.39405258917454
1997	9.982332777273335
1998	9.61073663291887
1999	8.65327912101555
2000	7.278131487489086
2001	6.604133387133326
2002	6.168066310393718
2003	5.818645602790892
2004	5.586808823073184
2005	5.151570318688834
2006	4.508349950149551
2007	4.4799999999999995
2008	4.564300521838587
2009	4.822049455615995
2010	4.286382549178915
2011	4.335699899498299
2012	4.090638853088927
2013	3.7604886475814414
2014	3.60345318280998
2015	3.2885680775076276
2016	2.839255036982195
2017	2.4630914219551494
2018	2.1568261880697484
2019	1.8928508455806157
2020	1.7301473852576958
2021	1.423664663311988
2022	1.2854263014348393