Year	Percent
1960	5.39055
1961	5.64687
1962	5.90606
1963	6.17222
1964	6.65121
1965	7.17122
1966	7.7415
1967	8.36178
1968	9.02869
1969	9.72836
1970	10.45793
1971	11.2148
1972	12.00675
1973	12.83671
1974	13.72291
1975	14.61768
1976	15.2844
1977	15.9852
1978	16.72926
1979	16.6999
1980	16.68158
1981	16.67146
1982	16.67434
1983	16.69289
1984	16.73217
1985	16.79125
1986	16.87501
1987	16.98042
1988	17.07339
1989	17.10252
1990	17.13475
1991	17.16943
1992	17.21184
1993	17.26454
1994	17.3366
1995	17.43202
1996	17.54948
1997	17.68637
1998	17.85411
1999	17.95209
2000	18.02347
2001	18.13827
2002	18.29097
2003	18.4656
2004	18.64269
2005	18.80522
2006	18.95143
2007	19.08259
2008	19.19808
2009	19.29591
2010	19.37908
2011	19.44568
2012	19.49743
2013	19.53778
2014	19.57607
2015	19.61651
2016	19.66073
2017	19.70793