Year	%
1977	62.88375
1978	62.80867
1979	62.63266
1980	62.17803
1981	59.72611
1982	60.38547
1983	59.16115
1984	58.63105
1985	60.55999
1986	61.65325
1987	62.21597
1988	62.95909
1989	63.09849
1990	63.16509
1991	63.47563
1992	63.3741
1993	63.2187
1994	64.13029
1995	65.03105
1996	65.87875
1997	66.2599
1998	67.66821
1999	67.76976
2000	69.03991
2001	71.24712
2002	73.0253
2003	74.62214
2004	75.84868
2005	76.9139
2006	78.17931
2007	78.60962
2008	77.90941
2009	78.62258
2010	78.81275
2011	79.98915
2012	78.38436
2013	79.46845
2014	79.12889
2015	80.33537
2016	79.4072
2017	79.66393