Year	% of total
1971	37.33226717860019
1972	37.93027722914275
1973	35.00600675748552
1974	40.124191788072395
1975	40.760118218459084
1976	42.233414144664536
1977	41.86909672647498
1978	37.8914953835982
1979	35.8967494573783
1980	31.010722722274792
1981	29.65598512012341
1982	28.39068333390435
1983	27.2692696664656
1984	27.89227879293318
1985	28.15995662844792
1986	28.324607060654618
1987	30.255485853428212
1988	31.430585848467306
1989	32.53442376905497
1990	34.451161282787126
1991	36.877377195017566
1992	38.13930698903002
1993	38.22507962470191
1994	38.056917242667254
1995	36.35382292487091
1996	36.11309161628276
1997	36.490511305508605
1998	36.864548173146524
1999	37.63584379555853
2000	38.3603115505221
2001	36.386022193059304
2002	35.7086222706204
2003	36.444898039133655
2004	38.082258821514344
2005	40.688889880595404
2006	40.04450468876718
2007	39.861804099227726
2008	38.28151122495777
2009	38.26041410441835
2010	36.15666204822486
2011	37.55393034711243
2012	36.72864987832694
2013	36.31175694702574
2014	35.53268795708443
2015	33.470014670240886