Year	% of revenue
1972	2.639751552795031
1973	2.843137254901961
1974	1.9094380796508457
1975	1.6956521739130437
1976	3.0660377358490565
1977	3.3847000550357733
1978	5.4362722704431246
1979	5.929078014184396
1980	3.853546031135883
1981	3.371357988810579
1982	5.3062817011314865
1983	7.704209915543808
1984	7.968382824182867
1985	7.956946970069298
1986	11.841117989120239
1987	13.861426092570921
1988	18.27881102623713
1989	16.564121953734574
1990	12.715462771066067
1991	10.75562890486856
1992	10.63421858031395
1993	11.264604566923541
1994	10.891003584745397
1995	8.86683579565239
1996	7.117146053229076
1997	9.501649982389063
1998	19.865142723527335
1999	21.605014417608665
2002	25.52539610553887
2003	18.708689806712815
2004	14.809910756622124
2008	9.001570012256488
2009	11.050663756961022
2010	8.88244114620184
2011	7.704470164481565
2012	7.512518871732015
2013	7.856606658789185
2014	8.592617946591849
2015	10.349568524975886
2016	11.745620752964552
2017	12.993120986703419
2018	13.274589994847826
2019	14.035658642781677
2020	19.085859666766815
2021	16.990143354225673
2022	12.945974704536015