Year	Percent
1960	16.15884
1961	15.3149
1962	15.09074
1963	13.68103
1964	15.99066
1965	16.98379
1966	15.07641
1967	15.57316
1968	17.25128
1969	17.31989
1970	16.90367
1971	16.84208
1972	17.54139
1973	16.76304
1974	16.69255
1975	21.92668
1976	25.06218
1977	30.03195
1978	31.556
1979	24.6664
1980	21.82672
1981	21.91699
1982	24.77954
1983	11.20344
1984	18.77837
1985	18.06574
1986	20.24457
1987	23.37281
1988	27.23035
1989	21.08788
1990	20.18409
1991	26.2269
1992	28.90875
1993	27.18119
1994	22.29927
1995	21.816
1996	21.32725
1997	21.98603
1998	22.67891
1999	19.15852
2000	18.113
2001	19.40564
2002	18.14214
2003	16.72362
2004	19.1691
2005	20.46868
2006	22.14697
2007	25.06856
2008	21.00734
2009	20.44941
2010	17.60649
2011	19.69511
2012	24.23255
2013	29.51278
2014	31.39699