Year	Percent
1960	11.15128
1961	11.49121
1962	11.83621
1963	12.19663
1964	12.57559
1965	12.97156
1966	13.38942
1967	13.82928
1968	14.29373
1969	14.78023
1970	15.24927
1971	15.69165
1972	16.15766
1973	16.6448
1974	17.15818
1975	17.6978
1976	18.26642
1977	18.86071
1978	19.48548
1979	20.13962
1980	20.82537
1981	21.53888
1982	21.80912
1983	21.70381
1984	21.6076
1985	21.51886
1986	21.4393
1987	21.368
1988	21.30444
1989	21.24584
1990	21.19301
1991	21.14478
1992	21.10239
1993	21.06685
1994	21.2785
1995	21.57829
1996	21.8974
1997	22.23208
1998	22.58294
1999	22.94567
2000	23.31893
2001	23.69924
2002	24.09079
2003	24.37455
2004	24.61694
2005	24.86734
2006	25.12862
2007	25.39984
2008	25.68214
2009	25.97317
2010	26.27581
2011	26.58956
2012	26.91575
2013	27.2524
2014	27.60314
2015	27.96771
2016	28.34764
2017	28.74028