Year	% of revenue
1972	36.206896551724135
1973	39.705882352941174
1974	41.05263157894737
1975	36.56716417910448
1976	39.411764705882355
1977	38.589211618257266
1978	40.993788819875775
1979	39.863325740318906
1980	34.17533432392273
1981	34.78260869565217
1982	27.95484727755644
1983	23.360378634212307
1984	26.108480413258718
1985	26.056531284302963
1986	28.659581762084336
1987	25.079651144080067
1988	30.342955835183815
1989	29.830520183296105
1990	30.60516442286471
1991	31.281800876094234
1992	33.395192291067524
1993	36.97485724663615
1994	34.984574079743766
1995	27.093532961402712
1996	26.594305457270117
1997	30.91684252613304
1998	36.27586977739367
1999	36.51059762765808
2000	34.11561520811231
2008	24.666012029412546
2009	27.49034333718387
2010	28.28401042200862
2011	27.852030984762756
2012	27.07745799073125
2013	31.27241657226519
2014	30.51459995172749
2015	34.72228312474566
2016	35.70618754086649
2017	35.756475422931935
2018	37.703936915159744
2019	36.399517235233304
2020	39.364889250601166
2021	38.855859437135784
2022	40.076943990690815