Year	Percent
1960	21.81638
1961	21.64387
1962	21.44771
1963	23.88055
1964	23.09613
1965	24.35897
1966	25.32526
1967	24.38848
1968	22.61808
1969	20.34264
1970	20.11782
1971	23.95535
1972	16.77934
1973	13.154
1974	15.04551
1975	10.91543
1976	9.60651
1977	7.79848
1978	18.8625
1979	17.53135
1980	26.03225
1981	22.05937
1982	17.52009
1983	13.6438
1984	14.32516
1985	15.00833
1986	15.23828
1987	18.04329
1988	17.77737
1989	18.09323
1990	19.36882
1991	21.93777
1992	24.29106
1993	21.17731
1994	19.09883
1995	20.83115
1996	23.42437
1997	20.79905
1998	20.40487
1999	23.77314
2000	22.09762
2001	23.81189
2002	25.06451
2003	25.199
2004	22.76321
2005	24.81459
2006	28.35787
2007	30.05235
2008	31.97813
2009	29.47677
2010	28.58802
2011	33.91887
2012	33.12177
2013	30.5985
2014	28.14627
2015	29.22012
2016	28.6401
2017	25.90607