Year	Number of Years
1960-01-01	60.068
1961-01-01	60.503
1962-01-01	60.924
1963-01-01	61.331
1964-01-01	61.725
1965-01-01	62.107
1966-01-01	62.477
1967-01-01	62.835
1968-01-01	63.181
1969-01-01	63.517
1970-01-01	63.843
1971-01-01	64.158
1972-01-01	64.462
1973-01-01	64.755
1974-01-01	65.038
1975-01-01	65.312
1976-01-01	65.577
1977-01-01	65.833
1978-01-01	66.081
1979-01-01	66.322
1980-01-01	66.557
1981-01-01	66.787
1982-01-01	67.012
1983-01-01	67.233
1984-01-01	67.449
1985-01-01	67.660
1986-01-01	67.864
1987-01-01	68.060
1988-01-01	68.247
1989-01-01	68.427
1990-01-01	68.600
1991-01-01	68.765
1992-01-01	68.925
1993-01-01	69.083
1994-01-01	69.241
1995-01-01	69.402
1996-01-01	69.570
1997-01-01	69.748
1998-01-01	69.934
1999-01-01	70.131
2000-01-01	70.337
2001-01-01	70.551
2002-01-01	70.770
2003-01-01	70.991
2004-01-01	71.213
2005-01-01	71.438
2006-01-01	71.667
2007-01-01	71.903
2008-01-01	72.142
2009-01-01	72.383
2010-01-01	72.618
2011-01-01	72.840
2012-01-01	73.044
2013-01-01	73.227
2014-01-01	73.388
2015-01-01	73.531
2016-01-01	73.659