Year	% of revenue
1972	13.54306113342258
1973	11.601216814159292
1974	13.817698259187623
1975	13.130731744752696
1976	16.99463327370304
1977	14.399487058347113
1978	14.499190964180336
1979	12.600043598766778
1980	13.53305187669886
1981	13.809884286795718
1982	15.09871373018247
1983	13.827031394823774
1984	14.894222767290088
1990	19.92723158307783
1991	19.452133744407686
1992	20.881028072059866
1993	16.048153511937844
1994	19.27072464183937
1995	15.17025429676534
1996	17.49584480221939
1997	16.94946121616673
1998	19.7246750800307
1999	15.893156058323108
2000	19.559234095187787
2001	15.607519824115542
2002	16.526220344276105
2003	16.659659710880636
2004	16.93488456095101
2005	18.09284549470596
2006	19.230466686570388
2007	19.821979346991956
2008	22.67114462015125
2009	21.46158853497849
2010	21.280635061545876
2011	20.779294029539003
2012	20.528187617358647
2013	20.966219411359706
2014	20.680287268300695
2015	22.57341347865874
2016	22.5347676105778
2017	24.591797187528964
2018	24.509584697662792
2019	25.730191177954904
2020	22.003440522383784
2021	25.713742861198035
2022	22.536935569507204