Year	Number of Years
1960-01-01	48.602
1961-01-01	49.250
1962-01-01	49.863
1963-01-01	50.437
1964-01-01	50.970
1965-01-01	51.460
1966-01-01	51.907
1967-01-01	52.317
1968-01-01	52.696
1969-01-01	53.049
1970-01-01	53.380
1971-01-01	53.691
1972-01-01	53.987
1973-01-01	54.270
1974-01-01	54.544
1975-01-01	54.815
1976-01-01	55.087
1977-01-01	55.361
1978-01-01	55.632
1979-01-01	55.895
1980-01-01	56.143
1981-01-01	56.372
1982-01-01	56.571
1983-01-01	56.729
1984-01-01	56.835
1985-01-01	56.877
1986-01-01	56.844
1987-01-01	56.736
1988-01-01	56.553
1989-01-01	56.295
1990-01-01	55.954
1991-01-01	55.521
1992-01-01	55.008
1993-01-01	54.438
1994-01-01	53.842
1995-01-01	53.247
1996-01-01	52.677
1997-01-01	52.164
1998-01-01	51.748
1999-01-01	51.473
2000-01-01	51.397
2001-01-01	51.577
2002-01-01	52.017
2003-01-01	52.703
2004-01-01	53.608
2005-01-01	54.687
2006-01-01	55.881
2007-01-01	57.115
2008-01-01	58.321
2009-01-01	59.452
2010-01-01	60.473
2011-01-01	61.370
2012-01-01	62.169
2013-01-01	62.890
2014-01-01	63.536
2015-01-01	64.112
2016-01-01	64.625