Year	% of revenue
1972	6.628571428571428
1973	7.39100817438692
1974	7.197625525599801
1975	8.919722497522299
1976	9.552350627458326
1977	8.89628924833492
1978	10.524977755179865
1979	10.32740288451416
1980	9.102167182662539
1981	8.760219005475136
1982	8.866489618541767
1983	8.346822056760548
1984	7.822965459878299
1985	7.175022515761033
1986	7.1746454269433935
1987	8.763091082196128
1988	8.20884699057288
1989	10.597471983320302
1990	12.9500221141088
1991	12.122849424143324
1992	11.680883826656565
1993	11.349269943019943
1994	13.500587848474582
1995	14.926211411085719
1996	16.791543548614044
1997	16.77982223096855
1998	16.599628942486085
1999	16.830604108322873
2000	16.969247869581327
2001	16.9173680452316
2002	17.072255515456522
2003	18.641069391087708
2004	17.721213757981445
2005	17.468512939639215
2006	18.173051562706053
2007	18.135179817180305
2008	17.305111439304337
2009	20.191460827330324
2010	21.1426937063318
2011	24.438158765004715
2012	25.460702160731664