Year	Percent
1960	10.42313
1961	10.51289
1962	10.54804
1963	10.57471
1964	10.58971
1965	10.6109
1966	10.64323
1967	10.6865
1968	10.73931
1969	10.79571
1970	10.91725
1971	11.04411
1972	11.09977
1973	11.14008
1974	11.16808
1975	11.19222
1976	11.22025
1977	11.25574
1978	11.29794
1979	11.34623
1980	11.43761
1981	11.49653
1982	11.51037
1983	11.53005
1984	11.55281
1985	11.57492
1986	11.59913
1987	11.62342
1988	11.64458
1989	11.66813
1990	11.72969
1991	11.76364
1992	11.70717
1993	11.65089
1994	11.60269
1995	11.56595
1996	11.53562
1997	11.50449
1998	11.4719
1999	11.44025
2000	11.42898
2001	11.4652
2002	11.55354
2003	11.62345
2004	11.68697
2005	11.73798
2006	11.77371
2007	11.77266
2008	11.74281
2009	11.74329
2010	11.77661
2011	11.82001
2012	11.87161
2013	11.93597
2014	11.99213
2015	12.03756
2016	12.0838
2017	12.12466