Year	% of revenue
1972	4.71707176481891
1973	4.47057166995213
1974	5.16475958231726
1975	7.94417971409122
1976	10.7965133754133
1977	13.6637931034483
1978	16.178386987789
1979	18.142780461621
1980	20.8857825482295
1981	22.5614579048945
1982	23.952931186122
1983	27.6833486062254
1984	28.0645424614296
1985	27.6621147675547
1986	27.8021846116913
1987	25.0148519052873
1988	23.237191796605
1989	22.3412284800345
1990	21.0555966905965
1994	18.9312431567698
1995	18.2856393803223
1996	18.1635911042683
1997	17.8598900495123
1998	19.017396481016
1999	19.3720757628201
2000	17.3699872104135
2001	16.3129623694683
2002	16.5507585201736
2003	15.7876779838355
2004	14.2739734915526
2005	12.3657162291646
2006	12.7944547453079
2007	13.8778171636424
2008	15.9323255712351
2009	17.3175344442878
2010	16.7199544889622
2011	16.336117010174
2012	15.5403904783056
2013	14.4409200522519
2014	13.2105765503802
2015	12.6780839791122
2016	12.6566933618825
2017	11.4630499425559