Year	Percent
1960	13.13878
1961	13.87897
1962	13.98191
1963	14.70021
1964	16.06381
1965	15.92724
1966	17.88553
1967	18.88138
1968	16.29886
1969	15.42809
1970	18.49366
1971	19.6928
1972	19.73825
1973	17.7428
1974	16.08931
1975	17.04014
1976	16.36445
1977	15.15722
1978	16.47969
1979	17.06
1980	19.74045
1981	18.58807
1982	21.2881
1983	21.48054
1984	19.54829
1985	19.74608
1986	21.28243
1987	22.36485
1988	22.65083
1989	21.7837
1990	26.26721
1991	24.59846
1992	24.442
1993	22.75389
1994	21.03982
1995	20.768
1996	20.41835
1997	23.65003
1998	22.77777
1999	21.90646
2000	21.50448
2001	21.27679
2002	21.10389
2003	21.07352
2004	22.01057
2005	22.81684
2006	23.53216
2007	23.27172
2008	24.39105
2009	25.04657
2010	22.40827
2011	24.20137
2012	23.80741
2013	25.95105
2014	27.41005
2015	25.77787
2016	27.51549
2017	27.38842