Year	% of revenue
1972	21.02857142857143
1973	18.29019073569482
1974	24.41256492703438
1975	21.268582755203173
1976	18.224386589248923
1977	17.174119885823025
1978	18.062793949408924
1979	22.62343404568902
1980	25.157010172490047
1981	23.693092327308182
1982	25.07242877836794
1983	21.107154418905793
1984	27.671496738607015
1985	26.607196466097697
1986	25.76633531589236
1987	25.694224055855287
1988	27.41479332849891
1989	26.446442533229085
1990	23.41736694677871
1991	18.148727427840182
1992	19.64656710580989
1993	20.08769586894587
1994	21.066895163700856
1995	17.420691792229924
1996	16.68425495989869
1997	13.834497687690641
1998	12.710946196660483
1999	11.339964407410983
2000	10.482809725185573
2001	10.254369227527595
2002	11.973424273526913
2003	11.949000847892307
2004	12.330484770153745
2005	10.808137635657507
2006	12.017835948832916
2007	11.375447596877386
2008	13.258121250375346
2009	10.58916346686588
2010	9.676804271141195
2011	11.448380030302605
2012	9.08590526598532