Year	% of revenue
1972	5.588235294117648
1973	6.685188400764018
1974	7.560483870967746
1975	8.850914667543005
1976	8.904710816346412
1977	11.420400381315531
1978	11.421056826332963
1980	16.36082401743654
1981	15.90553818669048
1982	16.029503428215257
1983	15.659660673588272
1984	15.155895106339049
1985	15.465854277735447
1986	15.617261183413255
1987	15.894881848044923
1988	14.020169216306286
1989	13.706200025118264
1990	14.101094319958312
1991	12.765890497168018
1992	14.55065120659971
1993	15.969752219266553
1994	15.89478102700436
1995	20.38191330343797
1996	21.950902459552974
1997	22.42423458387236
1998	22.821131811423072
1999	21.110798906439854
2000	21.549787535410765
2001	22.350147374062164
2002	21.555797869026105
2003	20.744535840188014
2004	19.824254429404643
2005	18.847008080908235
2006	18.40370178006516
2007	17.89486926049061
2008	18.47553673766145
2009	18.48162155271321
2010	17.895487867027324
2011	18.333145009416196
2012	17.981638619509415
2013	17.41670538262428
2014	16.771079649196324
2015	16.070799083681443
2016	16.371987604681536
2017	15.80565299514301
2018	15.700293568187885
2019	15.74027149321267
2020	17.866899727148706
2021	17.067146775126403
2022	17.084267531302817