Year	2011 U.S. Dollars
1980-01-01	30.42
1981-01-01	30.48
1982-01-01	30.61
1983-01-01	30.91
1984-01-01	31.92
1985-01-01	32.20
1986-01-01	32.96
1987-01-01	33.61
1988-01-01	33.61
1989-01-01	34.07
1990-01-01	34.18
1991-01-01	34.61
1992-01-01	35.38
1993-01-01	36.17
1994-01-01	37.14
1995-01-01	37.86
1996-01-01	38.44
1997-01-01	39.91
1998-01-01	40.93
1999-01-01	41.73
2000-01-01	43.17
2001-01-01	43.43
2002-01-01	45.14
2003-01-01	46.84
2004-01-01	48.41
2005-01-01	49.86
2006-01-01	51.32
2007-01-01	51.45
2008-01-01	50.49
2009-01-01	49.37
2010-01-01	50.80
2011-01-01	51.61