Year	% of revenue
1972	12.867981790591806
1973	12.401433691756273
1974	13.394603050449746
1975	12.491649966599866
1976	11.815864447443394
1977	10.080273720226346
1978	11.768646717284502
1979	11.74284652545522
1980	12.814279761077927
1981	11.86229262816515
1982	10.677639460388562
1983	10.315344304495724
1984	8.483795421923396
1985	8.584105520509492
1986	9.206206312221987
1987	7.216135920527342
1988	6.8970631859982205
1989	7.48227048207732
1990	8.303935224358556
1991	7.111116281234005
1992	9.0226410420959
1993	8.104488872123728
1994	7.045667947076398
1995	6.051881579712673
1996	6.82244804167385
1997	5.989282255222195
1998	5.294722036569673
1999	8.136088398599334
2000	7.384952759617159
2001	8.097730742268261
2002	6.5008709115540935
2003	7.646231286063411
2004	7.974515649407145
2005	8.816259791619133
2006	7.501704809909185
2007	7.179158299121974
2008	7.755945931745859
2009	10.732584754131276
2010	10.037435577120924
2011	10.213215033263072
2012	10.039112659784807
2013	11.193845116195947
2014	13.579124401717158
2015	13.859698488331967
2016	12.759065761408609
2017	12.707018910876473
2018	10.46956357065555
2019	12.04679410827792
2020	14.59933056680718
2021	12.20209858020175
2022	12.391964621644314