Year	Percent
1960	45.78824
1961	47.18644
1962	53.18083
1963	52.65943
1964	52.4748
1965	54.43835
1966	55.78789
1967	56.3528
1968	57.29532
1969	57.40919
1970	55.78756
1971	54.32441
1972	53.45085
1973	53.57477
1974	67.58835
1975	68.99267
1976	62.84888
1977	65.3087
1978	59.02509
1979	58.94933
1980	65.03131
1981	62.28918
1982	56.80968
1983	47.1375
1984	44.50713
1985	45.4422
1986	47.10905
1987	47.3637
1988	49.80916
1989	52.25871
1990	57.49329
1991	64.35226
1992	66.3567
1993	64.05866
1994	66.04206
1995	66.8471
1996	71.28692
1997	76.98827
1998	67.65286
1999	56.85377
2000	62.01058
2001	62.13544
2002	57.63981
2003	54.34003
2004	57.76765
2005	64.50079
2006	66.17346
2007	71.45837
2008	78.08938
2009	69.81378
2010	70.04226
2011	78.23036
2012	75.19115
2013	65.16164
2014	55.35747
2015	47.51941
2016	41.38008