Year	% of revenue
1972	15.010408181735905
1973	14.409636728663964
1974	6.969729043183742
1975	12.571707869215137
1976	11.818074702486154
1977	10.086239938673822
1978	9.922120594600573
1979	9.817220819121514
1980	9.972647984724157
1981	12.66026322729941
1982	11.852225548737119
1983	10.752305629293122
1984	11.299000768639509
1985	13.159708694218839
1986	13.041766499060731
1987	12.81814837522992
1988	10.095933328668828
1989	10.421143434880607
1990	10.098093822740353
1991	9.294989422985728
1992	11.1758270175648
1993	11.145034170354272
1994	10.4773356099785
1995	10.194577670175653
1996	10.064564441156863
1997	11.632817823176772
1998	13.215036497892523
1999	14.752476447000198
2000	13.164353483466277
2001	19.393477106677846
2002	13.891088324468189
2003	17.109162991011072
2004	14.132107114876256
2005	13.501701578515343
2006	11.97425815825415
2007	12.362690284404355
2008	13.69750656167979
2009	13.835152871118032
2010	15.037699562926262
2011	13.13258402672689
2012	14.116488972774102
2013	13.64768652893846
2014	14.967210697663875
2015	16.351197238086886
2016	17.507237150389653
2017	17.580914235294383
2018	18.522754585089235
2019	18.66777733896329
2020	20.246411355354688
2021	18.938646407009024
2022	17.46946471787199