Year	% of revenue
1972	6.928795175089999
1973	6.427810117241944
1974	8.284705712844897
1975	8.418201145286835
1976	9.226515784736064
1977	9.005951900029626
1978	8.229109153323572
1979	9.633252834513527
1980	11.233238074302045
1981	12.264961940636772
1982	14.684434741741331
1983	16.37482397599951
1984	17.204031629357388
1985	19.22926274559353
1986	18.79548519566987
1987	17.172627552702732
1988	17.47717049149672
1989	17.275810998041184
1990	18.08518477580045
1991	18.8798827282918
1992	18.739399813090582
1993	17.04680417868483
1994	16.108835356458343
1995	16.32096906842861
1996	16.491179911505004
1997	15.277919551341713
1998	14.089836620219916
1999	12.652407820495998
2000	11.205825739832926
2001	16.04028512308805
2002	15.85269053363198
2003	15.171976275346774
2004	14.867409814810209
2005	14.726729761020014
2006	14.456317121220188
2007	15.102001593717644
2008	14.839436864672642
2009	15.623791416194926
2010	15.448793777870756
2011	16.39415386714028
2012	15.520166012972958
2013	13.156018012416512
2014	13.218460459161557
2015	12.350294726133141
2016	13.026974161925489
2017	12.650507560510931
2018	14.97029778639383
2019	15.496675481499922
2020	13.755730541946717
2021	12.999282084111725
2022	14.4048381875285