Year	Number of Years
1960-01-01	42.292
1961-01-01	42.592
1962-01-01	42.883
1963-01-01	43.160
1964-01-01	43.418
1965-01-01	43.650
1966-01-01	43.847
1967-01-01	44.009
1968-01-01	44.141
1969-01-01	44.249
1970-01-01	44.338
1971-01-01	44.412
1972-01-01	44.485
1973-01-01	44.577
1974-01-01	44.709
1975-01-01	44.932
1976-01-01	45.300
1977-01-01	45.824
1978-01-01	46.485
1979-01-01	47.241
1980-01-01	48.085
1981-01-01	49.013
1982-01-01	49.934
1983-01-01	50.708
1984-01-01	51.177
1985-01-01	50.948
1986-01-01	49.579
1987-01-01	46.969
1988-01-01	43.264
1989-01-01	38.782
1990-01-01	34.217
1991-01-01	30.434
1992-01-01	28.102
1993-01-01	27.610
1994-01-01	29.003
1995-01-01	31.977
1996-01-01	35.923
1997-01-01	40.013
1998-01-01	43.596
1999-01-01	46.412
2000-01-01	48.415
2001-01-01	49.793
2002-01-01	50.970
2003-01-01	52.268
2004-01-01	53.755
2005-01-01	55.430
2006-01-01	57.219
2007-01-01	58.971
2008-01-01	60.565
2009-01-01	61.962
2010-01-01	63.140
2011-01-01	64.106
2012-01-01	64.911
2013-01-01	65.598
2014-01-01	66.188
2015-01-01	66.696
2016-01-01	67.129