Year	% of revenue
1973	12.72965879265092
1974	14.992577931716971
1975	20.414328873543376
1976	12.796486090775987
1977	13.563218390804598
1978	13.897220555888822
1979	14.86778646266423
1980	13.938657758882478
1981	16.091954022988507
1982	17.602765090729537
1983	15.230635335073977
1984	14.159400712268205
1985	14.748902974158948
1986	12.922061436912921
1987	13.21824272094821
1988	15.122956854660579
1989	14.622069523039613
1990	13.673774784885895
1991	16.23306693872924
1992	14.758076748066133
1993	15.563997442359048
1994	13.261558743212278
1995	11.90936371496872
1996	14.688231850117095
1997	9.803854291759592
1998	4.626172636060114
1999	4.373296448476466
2000	4.085097510666975
2001	3.8767273308969203
2002	1.8952884453623597
2003	1.1977450536408638
2004	3.679027686755807
2005	2.251035344476251
2012	3.634032752615537
2013	3.0895810413535925
2014	3.399391993717037
2015	3.3918558118431834
2016	3.496059066266067
2017	3.274173719674195
2018	3.722741284188638
2019	2.7911782524943582