Year	Number of Years
1960-01-01	42.609
1961-01-01	44.211
1962-01-01	45.833
1963-01-01	47.415
1964-01-01	48.914
1965-01-01	50.303
1966-01-01	51.581
1967-01-01	52.778
1968-01-01	53.921
1969-01-01	55.011
1970-01-01	56.052
1971-01-01	57.046
1972-01-01	57.995
1973-01-01	58.902
1974-01-01	59.770
1975-01-01	60.600
1976-01-01	61.393
1977-01-01	62.150
1978-01-01	62.869
1979-01-01	63.548
1980-01-01	64.185
1981-01-01	64.771
1982-01-01	65.306
1983-01-01	65.793
1984-01-01	66.235
1985-01-01	66.644
1986-01-01	67.034
1987-01-01	67.413
1988-01-01	67.789
1989-01-01	68.160
1990-01-01	68.522
1991-01-01	68.864
1992-01-01	69.172
1993-01-01	69.439
1994-01-01	69.664
1995-01-01	69.850
1996-01-01	70.000
1997-01-01	70.127
1998-01-01	70.241
1999-01-01	70.352
2000-01-01	70.473
2001-01-01	70.616
2002-01-01	70.783
2003-01-01	70.970
2004-01-01	71.170
2005-01-01	71.362
2006-01-01	71.521
2007-01-01	71.629
2008-01-01	71.681
2009-01-01	71.679
2010-01-01	71.643
2011-01-01	71.598
2012-01-01	71.574
2013-01-01	71.592
2014-01-01	71.659
2015-01-01	71.776
2016-01-01	71.934