Year	Percent
1960	12.228
1961	12.618
1962	13.019
1963	13.43
1964	13.854
1965	14.287
1966	14.732
1967	15.188
1968	15.657
1969	16.135
1970	16.635
1971	17.174
1972	17.728
1973	18.294
1974	18.875
1975	19.47
1976	20.081
1977	20.703
1978	21.34
1979	21.992
1980	22.741
1981	24.039
1982	25.389
1983	26.788
1984	28.237
1985	29.728
1986	31.266
1987	32.846
1988	34.468
1989	36.123
1990	37.814
1991	39.334
1992	39.603
1993	39.872
1994	40.142
1995	40.413
1996	40.684
1997	40.955
1998	41.228
1999	41.5
2000	41.774
2001	42.048
2002	42.328
2003	42.615
2004	42.909
2005	43.21
2006	43.517
2007	43.831
2008	44.152
2009	44.479
2010	44.814
2011	45.154
2012	45.502
2013	45.856
2014	46.216
2015	46.583
2016	46.957
2017	47.337