Year	%
1971	64.43765
1972	63.25232
1973	61.94793
1974	61.4286
1975	60.44814
1976	60.03908
1977	59.0471
1978	59.11825
1979	59.145
1980	58.57075
1981	55.88468
1982	56.36137
1983	54.57535
1984	53.6102
1985	55.95285
1986	57.48299
1987	58.31603
1988	59.84558
1989	60.16927
1990	59.85105
1991	59.66505
1992	59.11799
1993	58.24851
1994	58.97092
1995	59.79934
1996	60.62533
1997	60.42282
1998	61.95257
1999	61.26666
2000	62.91247
2001	65.02149
2002	66.75026
2003	68.55805
2004	70.80166
2005	71.56785
2006	72.7933
2007	74.57409
2008	74.14089
2009	75.03544
2010	75.75382
2011	76.40196
2012	75.83233
2013	76.11218
2014	76.09965
2015	76.2868
2016	75.55608