Year	Percent
1960	12.86311
1961	12.86305
1962	13.20496
1963	14.34358
1964	12.71344
1965	12.12705
1966	13.00731
1967	13.4986
1968	13.2733
1969	14.54649
1970	14.98041
1971	14.86077
1972	15.55611
1973	18.01345
1974	22.34615
1975	18.72456
1976	21.2113
1977	20.49157
1978	19.64858
1979	21.38958
1980	22.85536
1981	23.688
1982	22.45592
1983	19.91674
1984	21.49576
1985	21.58956
1986	17.51215
1987	17.63164
1988	17.58606
1989	18.59208
1990	18.11685
1991	16.89329
1992	17.48717
1993	17.41255
1994	18.64006
1995	21.07551
1996	19.21991
1997	20.48147
1998	21.08729
1999	21.47468
2000	24.81673
2001	24.47647
2002	23.72624
2003	22.9079
2004	23.48074
2005	24.76215
2006	27.06431
2007	27.78645
2008	27.75346
2009	23.13252
2010	27.15739
2011	28.57664
2012	27.59852
2013	26.604
2014	26.45326
2015	26.99605
2016	26.54951
2017	28.21807