Year	Percent
1960	29.25295
1961	29.50133
1962	29.31194
1963	36.29756
1964	30.77962
1965	34.16723
1966	30.70908
1967	31.98198
1968	35.78817
1969	37.27326
1970	40.36096
1971	37.0839
1972	36.63171
1973	39.02708
1974	40.54738
1975	38.01202
1976	36.54111
1977	42.75479
1978	42.13294
1979	41.41345
1980	44.2977
1981	33.15722
1982	31.06687
1983	29.80281
1984	25.60928
1985	22.98661
1986	23.40611
1987	20.55685
1988	17.61746
1989	26.41818
1990	30.50689
1991	24.18297
1992	26.35063
1993	19.26033
1994	24.23549
1995	29.5522
1996	28.48749
1997	29.7134
1998	29.83177
1999	26.06627
2000	32.94348
2001	34.72072
2002	31.6771
2003	30.55885
2004	28.01379
2005	31.18713
2006	34.75343
2007	39.73402
2008	41.37534
2009	30.72456
2010	34.46978
2011	38.57731
2012	37.07023
2013	34.5139
2014	36.49582
2015	33.08993
2016	26.77613
2017	25.54979