Year	% of revenue
1973	9.89010989010989
1974	6.762339639051968
1975	4.694640631491484
1976	4.85684588490976
1977	6.247869076031367
1978	9.464387002674012
1979	12.651622002820876
1980	17.868373145032272
1981	22.257597684515197
1982	28.059597151221215
1983	24.034306006901403
1984	23.78683499742041
1985	23.664325244785015
1986	21.43856189668218
1987	17.08439233437842
1988	13.160809435430762
1989	11.427495096192567
1990	14.856907967826514
1991	15.369043758536993
1992	12.889364388943456
1993	9.503102594605021
1994	9.326209683096113
1995	11.273707190612635
1996	13.3044230075362
1997	12.54580352469028
1998	13.1723701504162
1999	13.139939252542149
2000	11.933618504435994
2001	13.46569733564325
2002	12.542377694866397
2003	13.310667182351581
2004	13.688478407966636
2005	11.83633842589424
2006	12.022823081349921
2007	14.760599458695808
2008	13.712907399251268
2009	11.684870400713951
2010	10.612075196676594
2011	8.525237510242984
2012	8.107438553717436
2013	7.488810484584199
2014	7.499991744824832
2015	10.113467211987375
2016	10.160193855682843
2017	7.528570116439309
2018	7.305300015736996
2019	7.98549286756141
2020	9.006617612148947
2021	9.462006972240616
2022	8.030238239439074