Year	Percent
1960	10.642
1961	10.971
1962	11.309
1963	11.657
1964	12.014
1965	12.379
1966	12.747
1967	13.074
1968	13.41
1969	13.751
1970	14.1
1971	14.526
1972	14.964
1973	15.411
1974	15.869
1975	16.334
1976	16.755
1977	17.184
1978	17.622
1979	18.068
1980	18.524
1981	18.988
1982	19.461
1983	19.943
1984	20.434
1985	20.933
1986	21.442
1987	21.959
1988	22.487
1989	23.021
1990	23.566
1991	24.119
1992	24.681
1993	25.251
1994	25.536
1995	25.796
1996	26.058
1997	26.321
1998	26.586
1999	26.853
2000	27.121
2001	27.391
2002	27.663
2003	27.936
2004	28.211
2005	28.814
2006	29.425
2007	30.043
2008	30.67
2009	31.301
2010	31.938
2011	32.58
2012	33.227
2013	33.878
2014	34.534
2015	35.193
2016	35.856
2017	36.522