Year	% of revenue
1972	5.374677002583979
1973	5.078809106830122
1974	5.1035146846413095
1975	5.698497668796408
1976	6.3475409836065575
1977	6.18209067066317
1978	6.110916928812769
1979	6.899702992917524
1980	6.644981412639406
1981	6.937629278456359
1982	6.90094124861786
1983	6.621236894158539
1984	6.278512725456839
1985	6.607878735483127
1986	6.418612464303712
1987	6.513076801588785
1988	6.002991400752932
1989	6.326307635081934
1990	7.018692085441542
1991	4.2963476327630605
1992	3.670248364832295
1993	3.8707680617829405
1994	3.459027401610823
1995	3.342436304494756
1996	3.126798183996687
1997	3.052486636399655
1998	2.914392001183387
1999	2.7736805140362675
2000	3.1665246024249534
2001	3.3318179339999796
2002	3.3638648314377906
2003	2.2116055866588193
2004	1.9751834372650052
2005	1.4832490914047929
2006	0.7282934616432573
2007	1.0743488995415014
2008	0.9626586384970415
2009	1.9645723368727472
2010	2.935724404073945
2011	3.1805753091820974
2012	4.31502515630318
2013	4.4311008242908665
2014	8.765973654488187
2015	6.571620250126804
2016	34.00621101915501
2017	3.407927123778609
2018	3.293631383369708
2019	3.645102567309909
2020	4.484029251204515
2021	3.385726803519878
2022	3.1435240976413237