Year	% of total
1971	54.340438413615466
1972	56.19378830126458
1973	57.581853216667554
1974	59.59112220624371
1975	58.46875470121922
1976	59.769219603665036
1977	60.17123793472503
1978	59.48653648936093
1979	61.164896009259074
1980	62.210877203106996
1981	63.57207132836523
1982	63.35675127609366
1983	63.32651174289554
1984	64.74341372951916
1985	65.67048628418787
1986	63.9184049111517
1987	63.46403305445669
1988	63.2821054521161
1989	63.3776068942852
1990	64.59415820788477
1991	63.11360151522083
1992	62.47775996606949
1993	64.46829581583142
1994	63.17221585767496
1995	63.3405857760611
1996	63.462907237211155
1997	62.01521368783237
1998	60.20109341096098
1999	59.395649368195244
2000	58.94421614150864
2001	55.0746122660305
2002	55.729563373864025
2003	54.67228424008399
2004	54.65626632933693
2005	54.84176648602287
2006	55.38630876165005
2007	54.856290297338425
2008	54.02993678352439
2009	54.24702028027134
2010	53.02098881129924
2011	54.14796089492003
2012	51.02236348291787
2013	48.21868464224085
2014	46.45553776260643
2015	43.974658193795875