Year	Percent
1960	24.30123
1961	21.75969
1962	20.21695
1963	19.7196
1964	18.92804
1965	17.12535
1966	21.65874
1967	17.58278
1968	20.30766
1969	20.17195
1970	21.80635
1971	20.65628
1972	19.21729
1973	21.61838
1974	25.10746
1975	22.59625
1976	23.04678
1977	21.99891
1978	25.70893
1979	24.24696
1980	25.93655
1981	22.30658
1982	21.82301
1983	20.56297
1984	20.80876
1985	22.04651
1986	25.65358
1987	24.64445
1988	25.6015
1989	27.11426
1990	30.67969
1991	29.43291
1992	27.25875
1993	30.36779
1994	24.84716
1995	25.84553
1996	24.97939
1997	25.22044
1998	25.88991
1999	25.79881
2000	24.60691
2001	25.5836
2002	25.14168
2003	28.48225
2004	28.16078
2005	28.92507
2006	31.09238
2007	30.31989
2008	31.68044
2009	28.12
2010	27.94209
2011	33.13729
2012	32.23853
2013	31.09497
2014	31.43493
2015	30.89551
2016	27.36492
2017	27.1275