Year	Number of Years
1960-01-01	45.638
1961-01-01	46.145
1962-01-01	46.665
1963-01-01	47.207
1964-01-01	47.781
1965-01-01	48.407
1966-01-01	49.105
1967-01-01	49.883
1968-01-01	50.744
1969-01-01	51.682
1970-01-01	52.693
1971-01-01	53.765
1972-01-01	54.876
1973-01-01	56.001
1974-01-01	57.120
1975-01-01	58.216
1976-01-01	59.274
1977-01-01	60.291
1978-01-01	61.263
1979-01-01	62.181
1980-01-01	63.041
1981-01-01	63.840
1982-01-01	64.586
1983-01-01	65.285
1984-01-01	65.938
1985-01-01	66.548
1986-01-01	67.115
1987-01-01	67.640
1988-01-01	68.129
1989-01-01	68.586
1990-01-01	69.017
1991-01-01	69.428
1992-01-01	69.822
1993-01-01	70.201
1994-01-01	70.567
1995-01-01	70.922
1996-01-01	71.266
1997-01-01	71.594
1998-01-01	71.902
1999-01-01	72.187
2000-01-01	72.440
2001-01-01	72.651
2002-01-01	72.820
2003-01-01	72.948
2004-01-01	73.041
2005-01-01	73.112
2006-01-01	73.176
2007-01-01	73.245
2008-01-01	73.331
2009-01-01	73.440
2010-01-01	73.574
2011-01-01	73.730
2012-01-01	73.896
2013-01-01	74.066
2014-01-01	74.234
2015-01-01	74.400
2016-01-01	74.561