Year	% of revenue
1972	6.45770656964947
1973	5.573870573870588
1974	5.535327951031607
1975	6.3847389167356035
1976	6.54609616232907
1977	6.248524435350597
1978	6.968725216371825
1979	8.113041289023169
1980	8.490402905066546
1981	9.321236207708004
1982	9.190834318484788
1983	8.672540944354012
1984	8.25655951156531
1985	8.875913635217989
1986	8.609910543773253
1987	9.32507020431877
1988	8.950401206311607
1989	9.457954175449421
1990	9.281746852768457
1991	9.44990667666034
1992	9.407526020816642
1993	8.816369413694142
1994	9.120899260797842
1995	8.198245053814194
1996	7.067560772491999
1997	5.697740537612394
1998	5.548807906908448
1999	6.624983303696238
2000	7.004866270628477
2001	6.907311171569522
2002	7.488933793332644
2003	7.276461989199386
2004	7.615175644554059
2005	9.54813255765158
2006	9.741193410889402
2007	9.718212751262023
2008	9.162550080220496
2009	10.481426742449576
2010	9.812090699626935
2011	9.677233996358241
2012	9.533612714515716
2013	9.028856340481003
2014	8.706919357848394
2015	8.759582801510426
2016	9.46622644635591
2017	8.50876376310696
2018	8.661382028870234
2019	8.712735103345295
2020	8.685354737233872
2021	9.044275815831318
2022	8.814149441612658