Year	Number of Years
1960-01-01	63.879
1961-01-01	64.101
1962-01-01	64.307
1963-01-01	64.488
1964-01-01	64.644
1965-01-01	64.779
1966-01-01	64.903
1967-01-01	65.030
1968-01-01	65.169
1969-01-01	65.322
1970-01-01	65.486
1971-01-01	65.656
1972-01-01	65.821
1973-01-01	65.975
1974-01-01	66.116
1975-01-01	66.243
1976-01-01	66.360
1977-01-01	66.470
1978-01-01	66.578
1979-01-01	66.686
1980-01-01	66.793
1981-01-01	66.898
1982-01-01	67.000
1983-01-01	67.100
1984-01-01	67.199
1985-01-01	67.304
1986-01-01	67.417
1987-01-01	67.544
1988-01-01	67.687
1989-01-01	67.844
1990-01-01	68.014
1991-01-01	68.191
1992-01-01	68.370
1993-01-01	68.548
1994-01-01	68.727
1995-01-01	68.911
1996-01-01	69.108
1997-01-01	69.322
1998-01-01	69.556
1999-01-01	69.808
2000-01-01	70.070
2001-01-01	70.335
2002-01-01	70.593
2003-01-01	70.838
2004-01-01	71.067
2005-01-01	71.281
2006-01-01	71.485
2007-01-01	71.686
2008-01-01	71.887
2009-01-01	72.089
2010-01-01	72.285
2011-01-01	72.470
2012-01-01	72.638
2013-01-01	72.786
2014-01-01	72.913
2015-01-01	73.023
2016-01-01	73.120