Year	%
1971	64.42826
1972	63.24283
1973	61.93511
1974	61.41506
1975	60.43348
1976	60.02381
1977	59.03237
1978	59.10385
1979	59.1323
1980	58.55846
1981	55.87351
1982	56.35096
1983	54.56464
1984	53.60062
1985	55.94365
1986	57.47309
1987	58.3067
1988	59.83751
1989	60.16089
1990	59.84211
1991	59.65612
1992	59.11022
1993	58.24127
1994	58.96396
1995	59.79192
1996	60.61776
1997	60.41564
1998	61.94621
1999	61.26024
2000	62.90665
2001	65.01592
2002	66.74518
2003	68.55422
2004	70.79781
2005	71.56403
2006	72.78996
2007	74.57112
2008	74.13831
2009	75.03329
2010	75.7519
2011	76.40022
2012	75.83077
2013	76.1103
2014	76.09774
2015	76.28509
2016	75.55414