Year	% of revenue
1972	41.85441941074524
1973	45.540740740740745
1974	47.14424951267057
1975	48.646907216494846
1976	44.9438202247191
1977	44.57794417971409
1978	42.88932419196866
1979	43.833705357142854
1980	45.94835262689225
1981	44.75041012420905
1982	44.55696202531645
1983	45.76983709931687
1984	45.048357445448005
1985	43.23773475032756
1986	42.789898861395585
1987	39.55159373311724
1988	38.394361202234236
1989	33.985569759234565
1990	35.43980594918933
1991	33.618003783242465
1992	34.98950314905528
1993	34.854413741897936
1994	34.57346169945584
1995	33.1574045327538
1996	33.46711501608996
1997	34.06656380868415
1998	28.737531573598513
1999	32.980178365364424
2000	30.26872760458163
2001	32.154415181559045
2002	32.21930257259553
2003	31.217392320120673
2004	30.300631306090864
2005	29.580001654789662
2006	27.911843799767276
2007	26.82273544573901
2008	26.701055961877458
2009	27.306173666903494
2010	28.10692006066588
2011	26.37339111464825
2012	22.471081268451513
2013	21.66473835238712
2014	21.807551984766153
2015	21.24603114012069
2016	21.915827982690033
2017	21.735893047005977
2018	21.125649780076703
2019	19.90261180823385
2020	19.551335129128596
2021	18.68369535696372
2022	16.892823143433493