Year	Percent
1970	59.79416
1971	60.08868
1972	61.97507
1973	61.05652
1974	62.24482
1975	61.17324
1976	62.49674
1977	63.72783
1978	63.86957
1979	64.3194
1980	64.60702
1981	65.44931
1982	65.99299
1983	67.05315
1984	66.86575
1985	64.28224
1986	64.28677
1987	65.02732
1988	68.34698
1989	68.24592
1990	69.23885
1991	67.74462
1992	68.35209
1993	66.60799
1994	67.30454
1995	66.85162
1996	66.92893
1997	68.69319
1998	68.66265
1999	67.5967
2000	69.02153
2001	71.03644
2002	71.83612
2003	70.35216
2004	70.81596
2005	71.23866
2006	72.07485
2007	73.4483
2008	71.78489
2009	72.9732
2010	72.91322
2011	72.6024
2012	71.34065
2013	68.06768
2014	66.56702
2015	65.6763
2016	65.31421
2017	65.23071