Year	% of revenue
1974	14.361070816299618
1975	17.876975651431014
1976	19.10565204874772
1977	22.618326555334427
1978	19.906770594528503
1979	18.123375735193545
1980	18.8481995475943
1981	18.91712932307849
1982	20.710871104815865
1983	18.147218080514794
1984	20.971109165600378
1985	20.65100058125052
1986	20.97457627118644
1987	21.170388664476025
1988	20.25679649953375
1989	23.569462123678992
1990	20.141881312956368
1991	21.868589112066665
1992	24.176582869674696
1993	26.299769499005105
1994	25.07546251217137
1995	24.69922726103961
1996	25.062394191667973
1997	25.044528269397375
1998	26.48120999749705
1999	26.47658886479412
2000	24.91542423205203
2001	26.930399912961033
2002	25.412820380588936
2003	23.515957750156833
2004	21.078067106335986
2005	18.639881697997335
2006	16.653371053047742
2007	16.356579431013042
2008	14.080706696773007
2009	14.182631405239366
2010	21.158278585372138
2011	11.581768904684846
2012	13.949690242232169
2013	12.647243439194861
2014	13.559846863623276
2015	14.86263851823463
2016	13.224876660006013
2017	10.545006402930202
2018	8.863900136899781