Year	Percent
1960	28.27279
1961	23.97991
1962	16.63674
1963	16.89346
1964	16.05271
1965	22.23448
1966	23.86831
1967	25.81707
1968	22.26333
1969	20.81829
1970	22.75952
1971	18.63145
1972	19.83981
1973	27.21774
1974	26.4062
1975	33.06105
1976	37.45269
1977	29.07442
1978	20.50958
1979	30.99314
1980	32.75862
1981	31.37132
1982	24.96542
1983	21.38965
1984	27.42032
1985	35.79487
1986	40.13825
1987	31.10791
1988	21.14548
1989	22.23621
1990	31.1331
1991	41.15957
1992	52.49493
1993	41.50933
1994	27.22288
1995	33.22868
1996	31.85721
1997	31.88794
1998	28.92076
1999	24.99795
2000	23.77598
2001	22.06249
2002	20.96648
2003	20.98416
2004	23.60247
2005	24.78477
2006	28.36578
2007	24.66612
2008	23.94503
2009	26.17844
2010	25.24011
2011	23.88622
2012	24.83036
2013	18.59704
2014	28.6954
2015	32.27544
2016	29.62806
2017	30.07307