Year	Percent
1960	1.8439
1961	1.92127
1962	2.00166
1963	2.08505
1964	2.17193
1965	2.26184
1966	2.3557
1967	2.45335
1968	2.60901
1969	2.78318
1970	2.96776
1971	3.16282
1972	3.36973
1973	3.58866
1974	3.82288
1975	4.0738
1976	4.34348
1977	4.63124
1978	4.93968
1979	5.09261
1980	5.2181
1981	5.34526
1982	5.47559
1983	5.60943
1984	5.74827
1985	5.89136
1986	6.04126
1987	6.19713
1988	6.35678
1989	6.45686
1990	6.54183
1991	6.62039
1992	6.69542
1993	6.77205
1994	6.8596
1995	6.96265
1996	7.08307
1997	7.21666
1998	7.35995
1999	7.50574
2000	7.64951
2001	7.78883
2002	7.9261
2003	8.14271
2004	8.36809
2005	8.59248
2006	8.81739
2007	9.04251
2008	9.27052
2009	9.50189
2010	9.74079
2011	9.98742
2012	10.24262
2013	10.5041
2014	10.7732
2015	11.04997
2016	11.33481
2017	11.62857