Year	% of revenue
1972	4.761904761904762
1973	4.461852861035422
1974	4.180064308681672
1975	3.11199207135778
1976	3.3152275707061243
1977	3.3935934031081505
1978	3.800686411592729
1979	5.06369091483314
1980	4.458204334365325
1981	4.852621315532888
1982	5.776195074843072
1983	6.399050393870724
1984	6.8423587094514735
1985	8.071364240682763
1986	9.025495986357775
1987	10.274516026658203
1988	10
1989	10.317305186343498
1990	10.579389650597081
1991	11.517133513436656
1992	10.688534206731356
1993	11.402688746438747
1994	11.025646135145369
1995	12.300034860750667
1996	13.27388490220909
1997	12.934172980419167
1998	11.428571428571429
1999	11.567591430187482
2000	11.3426428690064
2001	10.359722336029591
2002	10.099438245648887
2003	9.466037202583454
2004	9.539150060765062
2005	9.63758121302312
2006	9.311947777924305
2007	8.762149058100484
2008	7.001342051561743
2009	6.943885450191612
2010	6.275962573035697
2011	5.582527687479771
2012	5.601521803266417