Year Number of Years 1960-01-01 32.292 1961-01-01 32.742 1962-01-01 33.185 1963-01-01 33.624 1964-01-01 34.060 1965-01-01 34.495 1966-01-01 34.928 1967-01-01 35.361 1968-01-01 35.796 1969-01-01 36.234 1970-01-01 36.678 1971-01-01 37.128 1972-01-01 37.587 1973-01-01 38.056 1974-01-01 38.540 1975-01-01 39.039 1976-01-01 39.556 1977-01-01 40.092 1978-01-01 40.650 1979-01-01 41.234 1980-01-01 41.853 1981-01-01 42.513 1982-01-01 43.217 1983-01-01 43.963 1984-01-01 44.747 1985-01-01 45.566 1986-01-01 46.417 1987-01-01 47.288 1988-01-01 48.164 1989-01-01 49.028 1990-01-01 49.856 1991-01-01 50.627 1992-01-01 51.331 1993-01-01 51.968 1994-01-01 52.539 1995-01-01 53.055 1996-01-01 53.533 1997-01-01 53.997 1998-01-01 54.468 1999-01-01 54.959 2000-01-01 55.482 2001-01-01 56.044 2002-01-01 56.637 2003-01-01 57.250 2004-01-01 57.875 2005-01-01 58.500 2006-01-01 59.110 2007-01-01 59.694 2008-01-01 60.243 2009-01-01 60.754 2010-01-01 61.226 2011-01-01 61.666 2012-01-01 62.086 2013-01-01 62.494 2014-01-01 62.895 2015-01-01 63.288 2016-01-01 63.673