Year	% of revenue
1972	7.067812798471825
1973	7.643840159177594
1974	6.953534031413606
1975	6.435199042202941
1976	6.658195679796698
1977	6.212518740629642
1978	8.542935310210957
1979	8.515155952555272
1980	9.733341012497863
1981	18.851490994980836
1982	17.058566953487446
1983	16.74980946442181
1984	17.07210742000181
1985	16.99840968552811
1986	16.862101313320828
1987	17.004277122820717
1988	16.391667911004955
1989	15.221104573922911
1990	15.493156086295285
1991	16.288637022516127
1992	15.410304797849827
1993	15.694818490836326
1994	14.974739087110775
1995	20.515650523155713
1996	21.198215970494893
1997	22.03573814295257
1998	21.69754931261207
1999	21.16556851414679
2000	19.466522157996145
2001	19.50334443632031
2002	19.340849956634866
2003	18.960859023207487
2004	20.633169241215416
2005	20.653427051954328
2006	19.175149115502915
2007	17.106242840778926
2008	18.270193191010932
2009	21.910633585730103
2010	22.06977934485896
2011	22.15995924605196
2012	21.795722820283416
2013	20.8391972098146
2014	20.929255465569447
2015	21.785925842347996
2016	22.375442788390004
2017	22.808542559473274
2018	22.72023273076555
2019	27.0711951600833
2020	29.475161233348796
2021	28.58460791959824
2022	28.23338245688667