Year	% of revenue
1972	19.299253302699597
1973	18.341968911917096
1974	16.750150270486877
1975	16.147888353061525
1976	21.961102106969204
1977	23.64069715477432
1978	23.939929328621908
1979	25.153709523158902
1980	22.06364309123586
1981	26.084747485011682
1982	33.37405326166626
1983	31.511710432931157
1984	33.964356435643566
1985	34.41993131148495
1986	34.73589607418604
1987	26.004042248011476
1988	21.230005630748057
1989	20.156061642719838
1990	22.97097683070274
1991	21.01378357860847
1992	26.153454817043798
1993	28.33883336103127
1994	33.98329930020776
1995	34.19341280758062
1996	34.02764566739771
1997	34.81142068829601
1998	35.68343841733923
1999	30.15786501788817
2000	25.652608515296212
2001	35.346658471066014
2002	35.61347967942506
2003	41.905194895232114
2004	41.210209077915295
2005	47.8797676656045
2006	53.9004743733752
2007	55.762486850332394
2008	57.816082995183514
2009	57.14098127158017
2010	57.09618735763146
2011	57.146808730215945
2012	54.6586827059719
2013	54.988393863910126
2014	52.69612961573792
2015	42.669105427429024
2016	48.976112905967426
2017	49.105933167889525
2018	52.058495639219394
2019	51.86103896033496
2020	48.48101320476626
2021	50.72995713232532
2022	51.02885031338862