Year	% of total
1971	67.88297450490963
1972	64.46062476495217
1973	64.86569033054766
1974	63.00342958502468
1975	62.90298164439469
1976	61.9327919533465
1977	60.31989889747733
1978	62.055988537446716
1979	61.44110474236112
1980	63.43045804639099
1981	64.93183963198653
1982	65.67219382410305
1983	67.01666278319361
1984	67.31231259111667
1985	65.98892737263913
1986	64.06343725924737
1987	66.50288651044231
1988	63.72205298611176
1989	63.64558884318122
1990	64.78644620848083
1991	64.03396132014858
1992	64.61904171250981
1993	66.35346923104842
1994	65.51109729285123
1995	64.75491725000758
1996	65.46557889156358
1997	65.27569086987197
1998	63.90208715065447
1999	62.75044571695678
2000	62.55823147918963
2001	62.01063290138523
2002	60.757331033462734
2003	62.3315994293825
2004	61.29790870619489
2005	61.091022526968544
2006	60.42832030991433
2007	60.7540365222216
2008	59.91837463032059
2009	58.47364012720043
2010	57.40244064995629
2011	56.52994147061676
2012	55.76651587397174
2013	54.12415323746262
2014	52.06778802116605
2015	51.063006736297986