Year	Number of Years
1990-01-01	68.084
1991-01-01	68.425
1992-01-01	68.748
1993-01-01	69.057
1994-01-01	69.355
1995-01-01	69.642
1996-01-01	69.912
1997-01-01	70.162
1998-01-01	70.387
1999-01-01	70.592
2000-01-01	70.778
2001-01-01	70.950
2002-01-01	71.115
2003-01-01	71.277
2004-01-01	71.440
2005-01-01	71.605
2006-01-01	71.773
2007-01-01	71.942
2008-01-01	72.110
2009-01-01	72.277
2010-01-01	72.444
2011-01-01	72.613
2012-01-01	72.783
2013-01-01	72.954
2014-01-01	73.126
2015-01-01	73.299
2016-01-01	73.473