Year	Number of Years
1960-01-01	49.969
1961-01-01	50.637
1962-01-01	51.264
1963-01-01	51.847
1964-01-01	52.385
1965-01-01	52.883
1966-01-01	53.349
1967-01-01	53.792
1968-01-01	54.215
1969-01-01	54.617
1970-01-01	54.987
1971-01-01	55.310
1972-01-01	55.576
1973-01-01	55.783
1974-01-01	55.937
1975-01-01	56.040
1976-01-01	56.097
1977-01-01	56.129
1978-01-01	56.164
1979-01-01	56.233
1980-01-01	56.378
1981-01-01	56.642
1982-01-01	57.042
1983-01-01	57.585
1984-01-01	58.267
1985-01-01	59.082
1986-01-01	60.011
1987-01-01	61.010
1988-01-01	62.032
1989-01-01	63.039
1990-01-01	63.990
1991-01-01	64.850
1992-01-01	65.609
1993-01-01	66.267
1994-01-01	66.818
1995-01-01	67.270
1996-01-01	67.640
1997-01-01	67.958
1998-01-01	68.253
1999-01-01	68.541
2000-01-01	68.834
2001-01-01	69.135
2002-01-01	69.440
2003-01-01	69.743
2004-01-01	70.048
2005-01-01	70.357
2006-01-01	70.668
2007-01-01	70.980
2008-01-01	71.291
2009-01-01	71.599
2010-01-01	71.902
2011-01-01	72.195
2012-01-01	72.479
2013-01-01	72.753
2014-01-01	73.015
2015-01-01	73.267
2016-01-01	73.512