Year	Percent
1960	36.83257
1961	35.13355
1962	34.53341
1963	34.79721
1964	35.62953
1965	35.88949
1966	34.97138
1967	33.60293
1968	34.43708
1969	36.66446
1970	36.75126
1971	35.45661
1972	34.97161
1973	39.45541
1974	50.12386
1975	42.62749
1976	43.20271
1977	42.10925
1978	41.15626
1979	46.31239
1980	45.93092
1981	44.97006
1982	48.23449
1983	51.71649
1984	51.83274
1985	52.44571
1986	47.14775
1987	47.22737
1988	46.73632
1989	46.78154
1990	43.30898
1991	38.91331
1992	37.86312
1993	44.12796
1994	53.64474
1995	55.0937
1996	52.70528
1997	56.09281
1998	57.41008
1999	56.6626
2000	61.59007
2001	57.87176
2002	56.2483
2003	56.06753
2004	58.6053
2005	62.37337
2006	65.5521
2007	66.01732
2008	68.45396
2009	58.33879
2010	62.96254
2011	64.63911
2012	61.92174
2013	56.70201
2014	56.96609
2015	55.94431
2016	54.48607
2017	57.06227