Year	% of revenue
1972	14.079422382671481
1973	9.454545454545455
1974	8.800880088008801
1975	5.023132848645076
1976	11.174785100286533
1977	11.352549889135254
1978	13.9649427785021
1979	6.569162121963313
1980	7.582107007114317
1981	6.752201430930105
1982	7.85917756190198
1983	9.022143445590034
1984	6.923577000866802
1985	9.213821190412856
1986	9.754809334092203
1987	10.466856012577978
1988	10.054003160429268
1989	11.631944444444445
1990	11.453914384882376
1991	10.22964509394572
1992	10.080800307810696
1993	16.109953247338478
1994	14.95880633281446
1995	9.572988488740272
1996	9.812320600574079
1997	11.082840930014564
1998	10.902271661765333
1999	5.571306627644656
2000	6.9238218205293744
2001	4.579082530894025
2002	6.50199859921625
2003	8.790796971948085
2004	3.9085288088773216
2005	1.5293931176785438
2006	2.4750593064537583
2007	0.3481313871568328
2008	-3.136629923754839
2009	2.2593105469792074
2010	1.6960895787082895
2011	5.928699815300503
2012	5.384982594611111
2013	5.2260093702634824
2014	5.427903488995876
2015	5.476371478392688
2016	4.728195355124623
2017	4.946270149822405
2018	4.926456454500541
2019	4.936462496582479
2020	5.063465496542341