Year	2011 U.S. Dollars
1978-01-01	28.86
1979-01-01	29.16
1980-01-01	29.61
1981-01-01	30.07
1982-01-01	30.92
1983-01-01	31.55
1984-01-01	32.10
1985-01-01	33.00
1986-01-01	32.33
1987-01-01	32.90
1988-01-01	33.27
1989-01-01	33.35
1990-01-01	33.59
1991-01-01	34.03
1992-01-01	34.84
1993-01-01	36.33
1994-01-01	36.68
1995-01-01	36.53
1996-01-01	38.17
1997-01-01	38.79
1998-01-01	39.82
1999-01-01	40.92
2000-01-01	41.11
2001-01-01	42.88
2002-01-01	43.55
2003-01-01	43.75
2004-01-01	45.18
2005-01-01	44.75
2006-01-01	45.54
2007-01-01	46.97
2008-01-01	45.46
2009-01-01	46.77
2010-01-01	46.79
2011-01-01	46.84