Year	Number of Years
1960-01-01	56.752
1961-01-01	57.283
1962-01-01	57.775
1963-01-01	58.238
1964-01-01	58.678
1965-01-01	59.100
1966-01-01	59.500
1967-01-01	59.877
1968-01-01	60.233
1969-01-01	60.574
1970-01-01	60.910
1971-01-01	61.248
1972-01-01	61.598
1973-01-01	61.966
1974-01-01	62.360
1975-01-01	62.791
1976-01-01	63.271
1977-01-01	63.796
1978-01-01	64.354
1979-01-01	64.932
1980-01-01	65.506
1981-01-01	66.049
1982-01-01	66.541
1983-01-01	66.965
1984-01-01	67.315
1985-01-01	67.588
1986-01-01	67.789
1987-01-01	67.938
1988-01-01	68.060
1989-01-01	68.171
1990-01-01	68.292
1991-01-01	68.443
1992-01-01	68.630
1993-01-01	68.857
1994-01-01	69.125
1995-01-01	69.428
1996-01-01	69.756
1997-01-01	70.090
1998-01-01	70.416
1999-01-01	70.727
2000-01-01	71.019
2001-01-01	71.293
2002-01-01	71.556
2003-01-01	71.813
2004-01-01	72.062
2005-01-01	72.303
2006-01-01	72.532
2007-01-01	72.749
2008-01-01	72.952
2009-01-01	73.143
2010-01-01	73.325
2011-01-01	73.500
2012-01-01	73.673
2013-01-01	73.847
2014-01-01	74.022
2015-01-01	74.200
2016-01-01	74.381