Year	Percent
1960	27.25573
1961	28.8539
1962	26.47509
1963	27.58042
1964	30.57967
1965	31.58766
1966	31.94956
1967	29.80035
1968	27.96505
1969	29.48444
1970	30.84738
1971	30.99795
1972	31.15703
1973	32.17945
1974	38.66905
1975	29.86101
1976	29.65861
1977	31.31193
1978	32.57469
1979	37.60971
1980	42.39849
1981	43.61418
1982	44.99069
1983	47.12886
1984	52.18384
1985	49.18049
1986	43.59
1987	48.32564
1988	51.2042
1989	52.59236
1990	52.94607
1991	47.50321
1992	44.54443
1993	41.71793
1994	45.18626
1995	46.89012
1996	48.78096
1997	50.41599
1998	50.99794
1999	50.61332
2000	54.33979
2001	52.32471
2002	49.21745
2003	47.8633
2004	47.96037
2005	52.0305
2006	55.34613
2007	56.04851
2008	57.843
2009	47.53863
2010	53.3584
2011	58.19317
2012	60.32269
2013	61.2817
2014	61.95334
2015	61.18805
2016	60.02382
2017	64.38837