Year	Percent
1960	2.47005
1961	2.53246
1962	2.60653
1963	2.68253
1964	2.7603
1965	2.83905
1966	2.93155
1967	3.03882
1968	3.14833
1969	3.4265
1970	3.72603
1971	4.04736
1972	4.39278
1973	4.76328
1974	5.16453
1975	5.59976
1976	6.07386
1977	6.39411
1978	6.56223
1979	6.73061
1980	6.89792
1981	7.06065
1982	7.22156
1983	7.38664
1984	7.56522
1985	7.76173
1986	7.98127
1987	8.21444
1988	8.42893
1989	8.63325
1990	8.81708
1991	8.97489
1992	9.11102
1993	9.23187
1994	9.35047
1995	9.47414
1996	9.60528
1997	9.73881
1998	9.89968
1999	10.15824
2000	10.41161
2001	10.65753
2002	10.90026
2003	11.13929
2004	11.37605
2005	11.60926
2006	11.84086
2007	12.07187
2008	12.30926
2009	12.49521
2010	12.50769
2011	12.53436
2012	12.57313
2013	12.61739
2014	12.66236
2015	12.7033
2016	12.73953
2017	12.77289