Year	% of total
1971	4.5899060570980765
1972	4.287452108415558
1973	4.195278688107761
1974	4.04130571219095
1975	4.141344842889297
1976	3.992860075578633
1977	3.7591905610398033
1978	3.4612278940330117
1979	3.6467265524920918
1980	4.062617118356025
1981	4.335141139849956
1982	4.773294229932099
1983	4.6341106931373
1984	4.69334236469448
1985	4.5753200724221825
1986	4.51503348385734
1987	4.869181808191609
1988	5.194296635717164
1989	5.523121538712877
1990	21.86656641170449
1991	21.407501864214478
1992	20.57581450136715
1993	19.87291166554421
1994	18.657498222649064
1995	18.418031242376397
1996	18.627661833905993
1997	18.808430831442102
1998	19.042646685370848
1999	19.816671124792837
2000	19.889794147077804
2001	20.456278223483817
2002	20.677750830183427
2003	21.221102677912004
2004	21.009041423467792
2005	20.53738611482812
2006	19.881660284995224
2007	19.79370146568327
2008	19.945185280980542
2009	19.863004838566322
2010	19.976764107721518
2011	18.595608011479396
2012	18.363491308698734
2013	17.629902767612716
2014	17.953964940001647
2015	18.226047666356003