Year	% of revenue
1972	5.172224056344228
1973	5.314209059952534
1974	5.027340243205745
1975	5.614191251271618
1976	5.569135933680518
1977	6.038111619064862
1978	5.092305786147937
1979	5.799848369977256
1980	5.392670157068062
1981	5.372015546918378
1982	5.243919919728606
1983	4.680415068015347
1984	4.8460423656469
1985	5.149335815212793
1986	5.135159569659163
1987	4.498311464687587
1988	4.540480742637952
1989	4.249266894377876
1990	4.112221368178324
1991	3.395866075158653
1992	3.572208984110798
1993	3.5074260463974465
1994	3.223970442114199
1995	3.1137839872542328
1996	2.5013589997761647
1997	2.4483760467829305
1998	2.5648427159311726
1999	2.31456285814899
2000	2.213185904120522
2001	2.4037784098322157
2002	2.6502386434681835
2003	2.6098059482996505
2004	2.4508822479695676
2005	2.2212989005369472
2006	1.8543512922244056
2007	1.9662892067782947
2008	1.935767287729317
2009	2.0322759940023785
2010	1.8919344882386162
2011	1.8083501862857745
2012	2.019912471405623
2013	2.1721410497752456
2014	2.3805436044351396
2015	2.7337389449915324
2016	3.4050088050131646
2017	3.2392134511256767
2018	3.271353452122314
2019	3.100099940502347
2020	3.829271835702704
2021	3.3207147516472566
2022	2.724749634984853