Year	% of revenue
1972	5.713217074197017
1973	7.854390423874722
1974	7.9136949787479285
1975	7.266056304221102
1976	6.989005336591012
1977	6.980689989496646
1978	6.579926542957966
1979	7.73607302198027
1980	8.239906206492268
1981	9.093608840400757
1982	9.423750397962433
1983	11.126247474438253
1984	10.207150016705647
1985	10.166150735990904
1986	9.536248435734507
1987	8.753379789408894
1988	8.12408448216753
1989	7.968085614638574
1990	7.1837809955418
1991	10.666551694403726
1992	7.458204977328579
1993	7.906537072496789
1994	6.742831372843774
1995	7.384407365589149
1996	6.318830349731705
1997	6.337778685128587
1998	5.657637003071718
1999	5.597690591785855
2000	5.7048443529958375
2001	4.20952785156987
2002	4.3427512968425726
2003	4.350180266964239
2004	4.088323691918312
2005	3.943886727970078
2006	4.134203620853763
2007	4.444137946045399
2008	4.777995667190534
2009	7.678766401044111
2010	8.495582410212107
2011	7.854453980855333
2012	7.274202081823774
2013	9.700991130368186
2014	7.902721864505725
2015	6.881876138755798
2016	6.3605927118874
2017	6.0433161152575305
2018	5.915836943943631
2019	5.019961873218049
2020	4.7075575151639315
2021	4.8112197049766605
2022	4.322323860204245