Year	Percent
1960	20.2706
1961	22.20018
1962	21.95993
1963	21.57932
1964	18.7995
1965	18.99303
1966	19.16449
1967	20.17415
1968	18.87503
1969	16.82166
1970	15.57573
1971	14.77525
1972	14.39697
1973	15.34728
1974	21.34913
1975	21.35986
1976	19.68979
1977	22.11905
1978	19.52803
1979	18.58211
1980	22.12288
1981	22.71825
1982	22.25198
1983	21.50158
1984	17.37356
1985	18.73365
1986	18.07372
1987	14.68549
1988	18.1223
1989	11.20712
1990	13.77249
1991	14.319
1992	15.38979
1993	16.16461
1994	16.15151
1995	18.32733
1996	18.33768
1997	18.99229
1998	19.25012
1999	17.80889
2000	18.76966
2001	18.46302
2002	17.97437
2003	18.60994
2004	19.02384
2005	20.50856
2006	21.24842
2007	24.166
2008	28.70614
2009	21.66988
2010	23.84664
2011	25.48552
2012	25.17028
2013	24.97361
2014	24.21103
2015	23.86021
2016	22.81653
2017	22.60354