Year	Percent
1960	8.12274
1961	8.44079
1962	8.5288
1963	8.4743
1964	8.44938
1965	8.44599
1966	8.36082
1967	8.24953
1968	8.13405
1969	8.00693
1970	7.87981
1971	7.78965
1972	7.75439
1973	7.73456
1974	7.73408
1975	7.75914
1976	7.80098
1977	7.87505
1978	7.96958
1979	8.08101
1980	8.203
1981	8.33698
1982	8.46204
1983	8.65823
1984	8.87602
1985	9.0998
1986	9.32456
1987	9.54976
1988	9.78716
1989	10.0458
1990	10.32888
1991	10.77382
1992	11.26576
1993	11.79979
1994	12.3765
1995	13.00273
1996	13.68463
1997	14.42316
1998	15.23489
1999	16.13266
2000	17.12695
2001	17.79222
2002	18.29665
2003	18.82802
2004	19.38527
2005	19.96228
2006	20.56777
2007	21.20194
2008	21.86338
2009	22.55126
2010	23.2701
2011	23.8731
2012	24.41938
2013	24.97829
2014	25.54668
2015	26.12622
2016	26.70103
2017	27.27141