Year	Percent
1960	18.67541
1961	26.75789
1962	22.69223
1963	19.19497
1964	27.10974
1965	33.3689
1966	36.08734
1967	34.91092
1968	35.99596
1969	36.42211
1970	36.15965
1971	37.14302
1972	33.0277
1973	27.34422
1974	29.18683
1975	30.69124
1976	30.33884
1977	27.13219
1978	24.20022
1979	26.78124
1980	24.39257
1981	24.11626
1982	21.18544
1983	18.94844
1984	22.75285
1985	29.20971
1986	27.88412
1987	24.00173
1988	24.36679
1989	26.83244
1990	25.82949
1991	22.32951
1992	21.62846
1993	22.51236
1994	22.68245
1995	22.9668
1996	23.13258
1997	24.07347
1998	30.06597
1999	28.13808
2000	26.21394
2001	26.57108
2002	24.51329
2003	22.53436
2004	25.08107
2005	30.63555
2006	43.44982
2007	36.57204
2008	36.69982
2009	33.05834
2010	39.01316
2011	45.29436
2012	39.96146
2013	41.27181
2014	32.96015
2015	25.25626
2016	26.26661
2017	28.72691