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	9.398201071260662
1991	11.193335372667079
1992	9.210692607270616
1993	9.062710712383375
1994	8.397296798155757
1995	9.106910400327322
1996	8.241691536494109
1997	8.389816784499175
1998	7.913499103936851
1999	7.721925911248004
2000	7.922988913580124
2001	6.911575825446326
2002	6.738872258693242
2003	6.545171006123335
2004	5.7190365706726976
2005	5.514229212235449
2006	5.747645632929659
2007	6.177549755571761
2008	6.535823027230975
2009	7.470734380899891
2010	8.107913374101773
2011	7.908150968628397
2012	7.835302476298629
2013	8.797017876923956
2014	7.54867917456504
2015	7.194784136844099
2016	6.6971045493350765
2017	7.190912073194257
2018	7.193939458249833
2019	6.716793898497752
2020	5.914085268099392
2021	6.980848612535782
2022	5.472199176343439