Year	Percent
1960	11.53255
1961	11.06148
1962	5.16815
1963	9.06881
1964	12.25205
1965	5.27625
1966	12.7572
1967	8.77565
1968	10.86946
1969	9.01398
1970	12.84431
1971	14.41993
1972	16.51621
1973	20.0536
1974	28.99795
1975	22.54776
1976	22.17409
1977	23.49098
1978	21.86714
1979	30.06582
1980	30.47417
1981	27.63044
1982	22.37903
1983	27.74541
1984	27.31498
1985	23.77767
1986	20.4956
1987	24.5768
1988	25.04166
1989	26.08755
1990	27.30576
1991	28.35126
1992	30.30746
1993	26.75481
1994	26.51143
1995	26.31217
1996	25.82455
1997	27.85924
1998	52.96813
1999	35.51413
2000	40.97731
2001	39.03214
2002	32.68762
2003	30.47765
2004	32.21669
2005	34.06727
2006	31.03472
2007	29.43572
2008	29.80828
2009	24.15912
2010	24.29903
2011	26.32735
2012	24.59438
2013	23.92358
2014	23.66598
2015	21.16018
2016	19.12095
2017	20.37082