Year	Percent
1960	2.98675
1961	3.22279
1962	3.47591
1963	3.75586
1964	4.10282
1965	4.48139
1966	4.8973
1967	5.35274
1968	5.85023
1969	6.38735
1970	6.64896
1971	6.86073
1972	7.07453
1973	7.29055
1974	7.51361
1975	7.74532
1976	7.98785
1977	8.23916
1978	8.50068
1979	8.77029
1980	9.04835
1981	9.07752
1982	9.08474
1983	9.09616
1984	9.11615
1985	9.14582
1986	9.18622
1987	9.23563
1988	9.29444
1989	9.36093
1990	9.43577
1991	9.51854
1992	9.60871
1993	9.7001
1994	9.78787
1995	9.86772
1996	9.93837
1997	10.0005
1998	10.05996
1999	10.12225
2000	10.19159
2001	10.35929
2002	10.57615
2003	10.80022
2004	11.02976
2005	11.26058
2006	11.49503
2007	11.73239
2008	11.97127
2009	12.20674
2010	12.43953
2011	12.66824
2012	12.8941
2013	13.11983
2014	13.34905
2015	13.58447
2016	13.827
2017	14.07633