Year	Percent
1960	1.6982
1961	1.79859
1962	1.90429
1963	1.99149
1964	2.08292
1965	2.17847
1966	2.27906
1967	2.41256
1968	2.55456
1969	2.70475
1970	2.86464
1971	3.03454
1972	3.2154
1973	3.40622
1974	3.60808
1975	3.82076
1976	4.04505
1977	4.28028
1978	4.4235
1979	4.50342
1980	4.58556
1981	4.66881
1982	4.75378
1983	4.84038
1984	4.92924
1985	5.0194
1986	5.11186
1987	5.20561
1988	5.29892
1989	5.38601
1990	5.46928
1991	5.54808
1992	5.62317
1993	5.69385
1994	5.76181
1995	5.82725
1996	5.89052
1997	5.95075
1998	6.01016
1999	6.0697
2000	6.13054
2001	6.18032
2002	6.14276
2003	6.10502
2004	6.06655
2005	6.02613
2006	5.98462
2007	5.94207
2008	5.89869
2009	5.85372
2010	5.808
2011	5.76138
2012	5.71439
2013	5.66679
2014	5.61985
2015	5.57368
2016	5.52866
2017	5.48405