Year	% of revenue
1972	6.302294530185507
1973	6.0386791211682675
1974	5.69249710890269
1975	5.925208127674505
1976	6.548265230795954
1990	18.909127843986997
1991	35.160037566312155
1992	35.555872265693246
1993	28.87624644822952
1994	29.960356542380584
1995	29.285421131834553
1996	29.062405788362977
1997	29.890043377383236
1998	22.025302650234487
1999	16.44387900335198
2000	19.768254225577724
2001	18.413318380447812
2002	16.809836723433072
2003	18.472469509295305
2004	19.78662258426095
2005	16.181390176171924
2006	18.13237605010069
2007	18.988583070875194
2008	19.942716670064183
2009	19.71838478437193
2010	17.68334846728728
2011	18.18381175226868
2012	17.17379034878145
2013	17.818177354163065
2014	18.147818570360684
2015	18.792783601175447
2016	20.268551928728414
2017	19.8079577910009
2018	15.247634693567818
2019	15.206498151378165
2020	14.59209960888505
2021	15.848137756157254
2022	18.64605474776286