Year	Percent
1960	9.96564
1961	10.10425
1962	9.70948
1963	8.87748
1964	12.3652
1965	12.75168
1966	14.13978
1967	14.739
1968	15.71219
1969	15.71106
1970	16.27427
1971	14.69038
1972	16.25192
1973	15.74176
1974	16.013
1975	18.99188
1976	17.5
1977	17.52747
1978	17.89684
1979	23.31146
1980	20.22227
1981	19.59452
1982	19.09741
1983	19.36425
1984	17.97485
1985	19.48807
1986	19.34649
1987	21.87184
1988	20.81258
1989	23.72827
1990	24.70596
1991	24.39988
1992	28.37159
1993	22.07878
1994	19.32441
1995	17.36417
1996	17.51397
1997	16.81813
1998	16.53926
1999	16.5756
2000	16.15872
2001	15.1819
2002	16.80437
2003	17.97449
2004	15.64939
2005	14.86642
2006	16.30092
2007	18.07201
2008	16.0685
2009	15.33053
2010	15.2148
2011	15.41374
2012	15.0339
2013	14.78395
2014	14.64902
2015	14.80716
2016	14.6462
2017	14.35126