Year	% of total
1971	42.73537063238964
1972	39.49957747776349
1973	40.75846106581173
1974	37.34462279233296
1975	39.4018812304959
1976	38.17472118112756
1977	39.39037687366941
1978	44.41605394834222
1979	42.252407145895255
1980	40.808888662461044
1981	39.47899511828576
1982	36.31521381795474
1983	35.458138871055795
1984	34.67700738543251
1985	30.572349742354653
1986	29.722317870985655
1987	25.178170846364267
1988	27.023257052352502
1989	26.0884285604238
1990	27.05711492501836
1991	25.47558414298845
1992	23.692341741651106
1993	22.14837192436765
1994	24.01674206268748
1995	20.264015599664923
1996	18.105915705540117
1997	18.256594042953306
1998	18.72388208821834
1999	16.65259868695801
2000	14.540183954186253
2001	14.218853379404134
2002	13.359183921297655
2003	14.834918690949689
2004	15.04559988540689
2005	16.998503672374657
2006	17.38788955819484
2007	16.871394164673816
2008	15.297751629415258
2009	13.847197210547055
2010	14.429703993164592
2011	14.591822546381634
2012	12.502154778626151
2013	13.851002932337863
2014	12.422320385201582
2015	11.488586226305117