Year	Percent
1960	1.80046
1961	1.85338
1962	1.97235
1963	2.09849
1964	2.23139
1965	2.37009
1966	2.51476
1967	2.66667
1968	2.83123
1969	3.01459
1970	3.22385
1971	3.46368
1972	3.73544
1973	4.03414
1974	4.3193
1975	4.54078
1976	4.75869
1977	4.97374
1978	5.19074
1979	5.41531
1980	5.65293
1981	5.88621
1982	6.09457
1983	6.31272
1984	6.54041
1985	6.77572
1986	7.02075
1987	7.27666
1988	7.54687
1989	7.83295
1990	8.13978
1991	8.41859
1992	8.59955
1993	8.78951
1994	8.98747
1995	9.1913
1996	9.40172
1997	9.61847
1998	9.84456
1999	10.08123
2000	10.33082
2001	10.53477
2002	10.67649
2003	10.83007
2004	11.00025
2005	11.18839
2006	11.39786
2007	11.62689
2008	11.87161
2009	12.12388
2010	12.38035
2011	12.63873
2012	12.90039
2013	13.16737
2014	13.44312
2015	13.73028
2016	14.02974
2017	14.34079