Year	Percent
1960	10.66561
1961	10.63475
1962	10.60821
1963	10.57686
1964	10.53383
1965	10.46838
1966	10.41324
1967	10.35644
1968	10.28615
1969	10.18006
1970	10.11217
1971	10.02274
1972	9.93386
1973	9.80677
1974	9.70902
1975	9.58852
1976	9.47788
1977	8.86295
1978	8.29305
1979	8.20021
1980	8.11023
1981	8.00577
1982	7.90912
1983	7.79094
1984	7.66065
1985	7.50421
1986	7.36639
1987	7.22535
1988	5.99174
1989	2.40894
1990	2.38661
1991	2.36022
1992	2.34476
1993	2.37288
1994	2.44597
1995	2.54279
1996	2.65255
1997	2.73518
1998	2.77467
1999	2.75263
2000	2.69594
2001	4.32795
2002	5.12604
2003	5.06008
2004	5.00965
2005	4.96444
2006	4.91658
2007	4.87023
2008	4.84911
2009	4.84191
2010	4.85742
2011	4.87558
2012	4.87472
2013	4.83643
2014	4.74314
2015	4.62173
2016	4.49242
2017	4.37825