Year	Percent
1960	43.5113
1961	42.92051
1962	42.51464
1963	42.66686
1964	44.03418
1965	44.58952
1966	44.27259
1967	43.86951
1968	43.46573
1969	42.79061
1970	42.59992
1971	40.76009
1972	42.04524
1973	35.34824
1974	32.6427
1975	38.24474
1976	37.42563
1977	41.42814
1978	48.33397
1979	48.63032
1980	55.12955
1981	52.56014
1982	46.45943
1983	48.66025
1984	50.69551
1985	53.86004
1986	57.01355
1987	56.06012
1988	58.01304
1989	56.09066
1990	53.19814
1991	53.26108
1992	52.66093
1993	48.69342
1994	48.20515
1995	49.90411
1996	48.80973
1997	52.47647
1998	57.16843
1999	53.44095
2000	51.41664
2001	52.3211
2002	47.69838
2003	48.7705
2004	47.91809
2005	47.98122
2006	49.12533
2007	47.60777
2008	48.64234
2009	51.48072
2010	51.13731
2011	48.66971
2012	50.82932
2013	48.33741
2014	49.90447
2015	55.90624
2016	55.23957
2017	65.35021