Year	% of total
1971	9.645908504341069
1972	10.822387989434585
1973	12.058433680982292
1974	11.52911250853921
1975	11.75895306236567
1976	13.000844399334403
1977	12.706041326864712
1978	13.000385746048929
1979	13.106428770322957
1980	13.589396985472163
1981	12.691953577592106
1982	11.834363515372765
1983	11.667835674992087
1984	10.797912263706024
1985	9.337315725181842
1986	9.226501524447452
1987	8.684754498423185
1988	8.090374475885378
1989	7.74206606010131
1990	13.393111755855053
1991	13.01240762687083
1992	12.185028812862841
1993	11.403108608822544
1994	10.945402924310875
1995	10.495147649027462
1996	9.713385559383852
1997	9.403424810605774
1998	9.966866224911177
1999	9.06458140100086
2000	8.1893222270559
2001	7.458944357190483
2002	6.767480086059513
2003	5.941343728668256
2004	5.710040291958788
2005	4.594622439024023
2006	3.839339104551648
2007	3.1738637579220663
2008	2.8930571670668215
2009	2.5895195072086428
2010	2.4365421965239054
2011	2.62942962226703
2012	2.691405413842083
2013	2.361886366053468
2014	2.2764845339504487
2015	2.035144719993407