Year	%
1971	61.82187
1972	60.8501
1973	59.51674
1974	59.18618
1975	58.27159
1976	58.10432
1977	57.29202
1978	57.76685
1979	57.95878
1980	57.71117
1981	54.99844
1982	55.81011
1983	53.88145
1984	53.20878
1985	55.40552
1986	56.91251
1987	58.03858
1988	59.29573
1989	59.39906
1990	58.79406
1991	58.92401
1992	58.16287
1993	57.47691
1994	58.08663
1995	58.80514
1996	59.73775
1997	59.6134
1998	61.60074
1999	60.96788
2000	62.64033
2001	64.6441
2002	66.82666
2004	71.04979
2005	71.56869
2006	72.98822
2007	74.84173
2008	74.47254
2009	75.57841
2010	76.16229
2011	76.60497
2012	76.2187
2013	76.13674
2014	75.98971
2015	76.14322
2016	75.09058