Year	%
1971	61.82979
1972	60.85747
1973	59.52645
1974	59.19642
1975	58.28298
1976	58.11732
1977	57.30454
1978	57.77926
1979	57.97007
1980	57.72192
1981	55.00859
1982	55.8199
1983	53.89147
1984	53.21709
1985	55.41367
1986	56.9215
1987	58.047
1988	59.30297
1989	59.40664
1990	58.80217
1991	58.9321
1992	58.16989
1993	57.48308
1994	58.09297
1995	58.81189
1996	59.74458
1997	59.62041
1998	61.60661
1999	60.97393
2000	62.64561
2001	64.64931
2002	66.83128
2004	71.0533
2005	71.57224
2006	72.99132
2007	74.84451
2008	74.475
2009	75.58043
2010	76.16402
2011	76.60652
2012	76.22018
2013	76.13862
2014	75.99157
2015	76.14467
2016	75.09249