Year	Percent
1960	22.1058
1961	22.15279
1962	23.41716
1963	23.61252
1964	24.45286
1965	26.82989
1966	26.74226
1967	27.75216
1968	33.55249
1969	34.96833
1970	34.34818
1971	32.01685
1972	30.74071
1973	38.85137
1974	45.06607
1975	41.66844
1976	41.09683
1977	38.71804
1978	38.22553
1979	37.4117
1980	35.41607
1981	31.04416
1982	24.70452
1983	24.56361
1984	19.6775
1985	24.43616
1986	33.13651
1987	30.72708
1988	25.90473
1989	30.38606
1990	33.1376
1991	34.0428
1992	31.89288
1993	33.72466
1994	37.46712
1995	37.58626
1996	37.47482
1997	38.07878
1998	36.32814
1999	33.86813
2000	36.43763
2001	36.7621
2002	38.82115
2003	39.7625
2004	45.48096
2005	55.0581
2006	59.96643
2007	61.65947
2008	69.60703
2009	54.81719
2010	61.02985
2011	67.9611
2012	73.22358
2013	68.47644
2014	69.15488
2015	54.24613
2016	45.6062
2017	45.24563