Year	% of revenue
1974	44.07226691283133
1975	42.67407090986758
1976	42.356779579694845
1977	40.29592454789305
1978	42.679199144123494
1979	42.60703050198331
1980	41.39512135477166
1981	39.43360668262619
1982	37.353930594900845
1983	41.64247037589265
1984	39.16425348508317
1985	37.429765562290676
1986	36.00980765568463
1987	36.01791582075807
1988	35.56774980274012
1989	34.87611379177644
1990	35.8915383869314
1991	34.482318988398106
1992	33.23011005970028
1993	31.800271872968338
1994	31.269879909120412
1995	28.355189260146428
1996	27.35105386553106
1997	27.306725786576408
1998	28.874336590573584
1999	27.961197438825657
2000	28.926504652662246
2001	30.15006450209049
2002	30.36666494765613
2003	30.203715320820862
2004	29.714834195126482
2005	30.762289684712744
2006	28.49027428792325
2007	24.900256172287484
2008	26.264006172271493
2009	23.776401904675822
2010	21.67563443225621
2011	24.981882079639426
2012	26.00492108741699
2013	27.30042527981719
2014	25.557036927415393
2015	29.833006949864693
2016	32.93057846646643
2017	37.34565266283868
2018	40.867349883138246