Year	Percent
1960	14.88344
1961	14.84133
1962	17.22341
1963	17.38648
1964	19.62446
1965	20.91886
1966	22.98962
1967	20.99257
1968	17.73654
1969	18.9694
1970	18.59421
1971	17.71517
1972	12.84808
1973	23.98171
1974	31.49733
1975	21.41921
1976	17.32109
1977	25.62536
1978	12.33953
1979	-5.73974
1980	16.77885
1981	23.59402
1982	18.77747
1983	22.48171
1984	22.22851
1985	23.13861
1986	16.89278
1987	15.79869
1988	26.75106
1989	27.46168
1990	19.2758
1991	20.77638
1992	20.92481
1993	19.46602
1994	17.53132
1995	18.92908
1996	22.1768
1997	26.2856
1998	25.82443
1999	33.00268
2000	26.65475
2001	24.30691
2002	22.43231
2003	22.25051
2004	24.111
2005	25.88521
2006	28.25262
2007	31.30405
2008	33.60199
2009	23.20046
2010	24.83987
2011	30.98265
2012	31.01168
2013	30.90475
2014	28.87935
2015	32.70363
2016	30.7109
2017	28.98679