Year	% of revenue
1972	14.933333333333335
1973	15.054495912806539
1974	13.826366559485532
1975	14.727452923686817
1976	15.471061996628583
1977	13.79638439581351
1978	14.821405872632514
1979	13.201389619959997
1980	14.34763379035825
1981	15.225380634515862
1982	14.660791887976824
1983	13.537282831552822
1984	12.161274788775554
1985	14.264270703778358
1986	15.588736846483384
1987	13.285464931767693
1988	11.816533720087019
1989	12.311050299713317
1990	12.274804658705587
1991	14.306839186691311
1992	13.72668833866986
1993	15.538194444444445
1994	14.622481716916086
1995	15.636983383042184
1996	15.621922048684395
1997	18.20164649545738
1998	19.085714285714285
1999	19.08894008580849
2000	20.400914770476934
2001	21.394875156566425
2002	22.341047798783787
2003	22.78736745140321
2004	23.00584502015857
2005	26.189611992305178
2006	25.605795859158643
2007	27.413316331447806
2008	27.949602593407402
2009	27.334818963532864
2010	27.417566702531904
2011	27.842745434673493
2012	26.692323612169144