Year	Number of Years
1960-01-01	30.371
1961-01-01	30.579
1962-01-01	30.789
1963-01-01	31.012
1964-01-01	31.263
1965-01-01	31.572
1966-01-01	31.973
1967-01-01	32.481
1968-01-01	33.098
1969-01-01	33.812
1970-01-01	34.601
1971-01-01	35.435
1972-01-01	36.272
1973-01-01	37.073
1974-01-01	37.809
1975-01-01	38.468
1976-01-01	39.046
1977-01-01	39.555
1978-01-01	39.998
1979-01-01	40.365
1980-01-01	40.641
1981-01-01	40.808
1982-01-01	40.861
1983-01-01	40.796
1984-01-01	40.616
1985-01-01	40.312
1986-01-01	39.873
1987-01-01	39.318
1988-01-01	38.683
1989-01-01	38.010
1990-01-01	37.348
1991-01-01	36.746
1992-01-01	36.246
1993-01-01	35.888
1994-01-01	35.705
1995-01-01	35.729
1996-01-01	35.980
1997-01-01	36.432
1998-01-01	37.055
1999-01-01	37.822
2000-01-01	38.702
2001-01-01	39.660
2002-01-01	40.660
2003-01-01	41.669
2004-01-01	42.660
2005-01-01	43.624
2006-01-01	44.566
2007-01-01	45.500
2008-01-01	46.432
2009-01-01	47.348
2010-01-01	48.224
2011-01-01	49.034
2012-01-01	49.762
2013-01-01	50.401
2014-01-01	50.951
2015-01-01	51.423
2016-01-01	51.835