Year	Number of Years
1960-01-01	48.056
1961-01-01	48.623
1962-01-01	49.147
1963-01-01	49.641
1964-01-01	50.113
1965-01-01	50.556
1966-01-01	50.955
1967-01-01	51.302
1968-01-01	51.602
1969-01-01	51.874
1970-01-01	52.155
1971-01-01	52.487
1972-01-01	52.902
1973-01-01	53.414
1974-01-01	54.027
1975-01-01	54.723
1976-01-01	55.471
1977-01-01	56.228
1978-01-01	56.963
1979-01-01	57.665
1980-01-01	58.338
1981-01-01	59.001
1982-01-01	59.677
1983-01-01	60.378
1984-01-01	61.097
1985-01-01	61.812
1986-01-01	62.494
1987-01-01	63.117
1988-01-01	63.669
1989-01-01	64.151
1990-01-01	64.580
1991-01-01	64.987
1992-01-01	65.401
1993-01-01	65.840
1994-01-01	66.308
1995-01-01	66.789
1996-01-01	67.259
1997-01-01	67.690
1998-01-01	68.061
1999-01-01	68.368
2000-01-01	68.613
2001-01-01	68.807
2002-01-01	68.972
2003-01-01	69.127
2004-01-01	69.282
2005-01-01	69.444
2006-01-01	69.618
2007-01-01	69.797
2008-01-01	69.980
2009-01-01	70.167
2010-01-01	70.357
2011-01-01	70.550
2012-01-01	70.742
2013-01-01	70.933
2014-01-01	71.120
2015-01-01	71.304
2016-01-01	71.484