Year	% of revenue
1972	2.993831803821273
1973	3.310454115986748
1974	3.212290502793296
1975	3.573913411741929
1976	4.345922948267926
1977	4.847335996208788
1978	5.3907508527395915
1979	6.5690830905239235
1980	7.36210396251967
1981	6.88946861409573
1982	6.60253164556962
1983	7.293028225256238
1984	8.564451767882312
1985	10.859418106983611
1986	10.884353741496598
1987	10.62909619979444
1988	10.499867157551144
1989	9.995864817112139
1990	9.967994877117771
1991	9.77647265404632
1992	9.837301132174398
1993	9.784587899817927
1994	9.934385892966992
1995	10.053201582874983
1996	9.819299700416684
1997	10.236209688740066
1998	9.733783258941841
1999	8.07984254726699
2000	7.891931563748145
2001	6.654014472552748
2002	6.476219365314444
2003	6.067941799489761
2004	5.770585576029705
2005	5.01210228440838
2006	4.4488133227503015
2007	4.434276557279645
2008	5.82134744052886
2009	5.566324610164139
2010	5.6330293059159935
2011	5.8793144712725685
2012	5.999762564366986
2013	5.796226221956222
2014	5.3885969155140145
2015	5.071652519743119
2016	4.670808731970268
2017	4.138206670579482
2018	3.9147920070378284
2019	3.6999237729599135
2020	3.843998517336817
2021	3.2065611738579145
2022	3.3943167555337763