Year	Number of Years
1960-01-01	58.030
1961-01-01	59.134
1962-01-01	60.176
1963-01-01	61.124
1964-01-01	61.960
1965-01-01	62.677
1966-01-01	63.286
1967-01-01	63.815
1968-01-01	64.289
1969-01-01	64.718
1970-01-01	65.100
1971-01-01	65.431
1972-01-01	65.707
1973-01-01	65.933
1974-01-01	66.122
1975-01-01	66.297
1976-01-01	66.481
1977-01-01	66.690
1978-01-01	66.935
1979-01-01	67.219
1980-01-01	67.537
1981-01-01	67.874
1982-01-01	68.210
1983-01-01	68.528
1984-01-01	68.819
1985-01-01	69.083
1986-01-01	69.322
1987-01-01	69.545
1988-01-01	69.758
1989-01-01	69.958
1990-01-01	70.140
1991-01-01	70.298
1992-01-01	70.425
1993-01-01	70.520
1994-01-01	70.585
1995-01-01	70.620
1996-01-01	70.628
1997-01-01	70.618
1998-01-01	70.600
1999-01-01	70.587
2000-01-01	70.593
2001-01-01	70.635
2002-01-01	70.719
2003-01-01	70.846
2004-01-01	71.014
2005-01-01	71.218
2006-01-01	71.446
2007-01-01	71.683
2008-01-01	71.914
2009-01-01	72.130
2010-01-01	72.327
2011-01-01	72.501
2012-01-01	72.657
2013-01-01	72.802
2014-01-01	72.935
2015-01-01	73.060
2016-01-01	73.179