Year	% of revenue
1973	2.9800569800569816
1974	2.9518815192725505
1975	3.1347962382445194
1976	4.062229904926534
1977	4.2551614829559306
1978	4.65230166503428
1979	6.563298604285434
1980	7.287303664921466
1981	6.6440121865479265
1982	6.403903715069048
1983	7.131844631222957
1984	8.218582403246849
1985	10.859418106983611
1986	10.884353741496598
1987	10.62909619979444
1988	9.738594752234349
1989	9.654637990317202
1990	9.502062629802147
1991	7.4896358594686605
1992	7.6026394960962005
1993	6.794454903303112
1994	7.156284008838178
1995	8.852382351140962
1996	9.148829796742906
1997	9.839699099986566
1998	8.355156503304652
1999	7.850694443977162
2000	7.399838755559038
2001	6.634297735507971
2002	6.0983671625098035
2003	5.594670048295947
2004	4.916485443053649
2005	4.606635561456109
2006	4.32418424434238
2007	4.166980653920868
2008	3.494631468495344
2009	4.075435221371817
2010	4.394515775306727
2011	5.068163438266313
2012	4.993848075277539
2013	5.076309177377134
2014	4.991993320639781
2015	4.900218877091797
2016	4.469624975273003
2017	4.023460680134406
2018	3.675801395332405
2019	3.3932974093552684
2020	3.2935417340237683
2021	3.1087890099345623
2022	3.2166298766175014