Year	% of revenue
1973	33.72921615201907
1974	31.694560669456003
1975	29.13793757918021
1976	29.64467890191238
1977	29.598403388725913
1978	28.27383708210157
1979	28.205835243254523
1980	28.205745908550632
1981	27.49431954858299
1982	27.78747710604811
1983	28.161403005148422
1984	28.26353256360038
1985	28.350718079661654
1986	29.063908722722356
1987	28.26988215852441
1988	29.903489233830825
1989	29.59402903997472
1990	28.39991770470942
1991	25.889733948228066
1992	27.09830543445281
1993	28.387096774193544
1994	32.15058748964216
1995	30.53762493137152
1996	32.64868004823933
1997	29.68533857905557
1998	30.42583830487554
1999	31.86235981980255
2000	30.574899345095126
2001	31.228823509678282
2002	32.337941568809164
2003	32.810695892115525
2004	32.399346508769575
2005	33.24864125245578
2006	32.18452042546278
2007	32.71817593345776
2008	31.74908561030311
2009	30.822157302863847
2010	31.569942972156994
2011	31.466047405122012
2012	30.524154412324116
2013	29.89764660404968
2014	30.984673392048016
2015	31.369409148159846
2016	31.930180401473315
2017	32.4401268910614
2018	32.236599299466086
2019	32.273432793732944
2020	31.22402309572861
2021	30.885174884011867
2022	31.585597625038417