Year	Percent
1960	29.95325
1961	27.53754
1962	27.79267
1963	25.75681
1964	24.61552
1965	25.90302
1966	22.37016
1967	20.46033
1968	20.62144
1969	18.39248
1970	25.45375
1971	24.6121
1972	22.3257
1973	24.34797
1974	26.43137
1975	27.48993
1976	29.04678
1977	33.81493
1978	34.77089
1979	33.71065
1980	32.2185
1981	30.45938
1982	27.35646
1983	26.32873
1984	28.804
1985	26.01201
1986	23.7182
1987	25.19228
1988	26.07644
1989	27.2602
1990	30.1808
1991	28.74109
1992	31.77037
1993	33.80101
1994	33.81288
1995	35.59763
1996	34.97334
1997	36.53812
1998	36.24382
1999	35.4837
2000	39.0157
2001	37.33119
2002	34.91333
2003	34.6535
2004	35.3309
2005	32.33687
2006	30.12853
2007	29.115
2008	24.84149
2009	21.32837
2010	19.55232
2011	20.89684
2012	19.81648
2013	20.3204
2014	21.08876
2015	21.0131
2016	21.33284
2017	21.92947