Year	Percent
1960	39.11299
1961	22.28353
1962	15.32438
1963	21.2529
1964	23.83155
1965	26.64937
1966	30.1689
1967	23.72645
1968	24.78069
1969	24.76302
1970	32.67535
1971	33.33469
1972	30.99436
1973	32.78064
1974	33.10464
1975	34.94983
1976	33.12922
1977	33.78769
1978	38.40077
1979	37.06701
1980	35.38098
1981	33.68914
1982	32.74716
1983	32.69123
1984	35.17485
1985	39.8907
1986	38.56795
1987	38.15093
1988	39.92179
1989	37.90422
1990	34.73376
1991	35.86583
1992	39.83722
1993	44.24293
1994	40.94851
1995	39.68464
1996	38.37236
1997	36.33716
1998	35.67869
1999	34.96478
2000	34.42965
2001	36.42225
2002	37.07754
2003	40.63155
2004	42.89449
2005	41.39121
2006	40.93327
2007	41.46315
2008	43.26637
2009	46.4413
2010	47.61226
2011	47.68587
2012	47.23453
2013	47.38775
2014	47.00772
2015	45.40088
2016	44.26358
2017	43.60021