Year	% of total
1971	58.04003580119124
1972	55.248955163892056
1973	56.47414344001776
1974	53.95163784084519
1975	54.38246636061477
1976	51.74860433700324
1977	51.91932022611474
1978	51.22988596682527
1979	50.90649029233079
1980	46.36070537679491
1981	48.99894371052241
1982	49.26411122669005
1983	51.96909633632345
1984	49.94102622115801
1985	50.805124857724216
1986	50.219855894633156
1987	47.292199472109985
1988	47.60404513365334
1989	45.416438704537
1990	37.062488318874856
1991	37.57804117611749
1992	35.99589170678465
1993	32.65057023138106
1994	32.17779313319637
1995	32.29749234130316
1996	31.29787290631219
1997	31.530332427010443
1998	31.42724577590521
1999	31.672790492525284
2000	31.751004978560793
2001	29.49819170177087
2002	29.643728346664638
2003	28.298062411806757
2004	27.29814247992191
2005	24.27233225824452
2006	24.217309527940138
2007	24.510504724659192
2008	24.543602225993595
2009	22.49183079244603
2010	21.450446574905033
2011	23.292745167291795
2012	24.7385294531216
2013	24.029768374161982
2014	22.019005363902515
2015	18.519858843398698