Year	% of total
1971	44.50116618493449
1972	48.72322753618954
1973	53.62439958984091
1974	48.66410664901401
1975	47.658187312693904
1976	49.56240535855279
1977	49.06540090361846
1978	45.616730649554974
1979	42.96524816832495
1980	39.73366218617886
1981	38.235785860452225
1982	34.83341266846797
1983	31.721436988522772
1984	26.899479653094577
1985	21.418400452321023
1986	19.511451361126504
1987	18.39613021281107
1988	19.43337569632305
1989	19.89939490573897
1990	16.875934388146767
1991	16.621635882510706
1992	16.270969884348727
1993	15.226375664473938
1994	14.071641044004762
1995	13.495520733362765
1996	12.294413870317861
1997	11.635307696263563
1998	10.42208207947922
1999	9.69578939878642
2000	9.17975096602714
2001	8.130651201593139
2002	7.857120258995081
2003	7.340780719973164
2004	6.748384302988623
2005	5.962871835646291
2006	4.869650027316106
2007	4.4237130658397
2008	3.7586469954587574
2009	2.796657516407939
2010	2.6518028382875225
2011	2.9818701209435807
2012	2.881449641466107
2013	2.315119465535278
2014	1.940594454830618
2015	1.6807707865951735