Year	%
1974	60.44005
1976	59.7612
1977	59.78704
1978	59.72445
1979	59.71719
1980	58.83209
1981	54.99502
1982	54.96347
1983	54.94251
1984	53.34997
1985	57.32457
1986	58.51768
1987	58.42266
1988	59.0868
1989	61.11394
1990	61.48618
1991	59.97233
1992	61.50474
1993	59.59401
1994	61.50345
1995	63.3858
1996	64.7986
1997	64.40949
1998	67.04996
1999	66.26303
2000	68.06237
2001	69.27616
2002	70.77145
2003	72.66186
2004	74.4721
2005	75.69518
2006	77.09363
2007	78.33679
2008	75.64113
2009	75.80979
2010	77.05631
2011	77.9838
2012	75.38807
2013	75.76668
2014	75.13923
2015	75.76695
2016	74.83711