Year	Number of Years
1960-01-01	45.831
1961-01-01	46.460
1962-01-01	47.086
1963-01-01	47.694
1964-01-01	48.257
1965-01-01	48.690
1966-01-01	48.895
1967-01-01	48.838
1968-01-01	48.535
1969-01-01	48.050
1970-01-01	47.523
1971-01-01	47.136
1972-01-01	47.031
1973-01-01	47.291
1974-01-01	47.925
1975-01-01	48.865
1976-01-01	49.981
1977-01-01	51.098
1978-01-01	52.082
1979-01-01	52.878
1980-01-01	53.478
1981-01-01	53.917
1982-01-01	54.292
1983-01-01	54.678
1984-01-01	55.102
1985-01-01	55.578
1986-01-01	56.102
1987-01-01	56.654
1988-01-01	57.220
1989-01-01	57.800
1990-01-01	58.401
1991-01-01	59.033
1992-01-01	59.700
1993-01-01	60.400
1994-01-01	61.127
1995-01-01	61.868
1996-01-01	62.610
1997-01-01	63.338
1998-01-01	64.038
1999-01-01	64.702
2000-01-01	65.324
2001-01-01	65.903
2002-01-01	66.448
2003-01-01	66.965
2004-01-01	67.460
2005-01-01	67.937
2006-01-01	68.403
2007-01-01	68.861
2008-01-01	69.312
2009-01-01	69.759
2010-01-01	70.198
2011-01-01	70.626
2012-01-01	71.039
2013-01-01	71.431
2014-01-01	71.803
2015-01-01	72.155
2016-01-01	72.489