Year	2011 U.S. Dollars
1971-01-01	19.38
1972-01-01	19.84
1973-01-01	20.88
1974-01-01	20.76
1975-01-01	21.10
1976-01-01	21.85
1977-01-01	22.24
1978-01-01	22.83
1979-01-01	23.27
1980-01-01	23.29
1981-01-01	24.11
1982-01-01	25.20
1983-01-01	26.44
1984-01-01	26.55
1985-01-01	27.20
1986-01-01	28.28
1987-01-01	29.08
1988-01-01	29.60
1989-01-01	29.53
1990-01-01	30.15
1991-01-01	30.86
1992-01-01	32.01
1993-01-01	33.38
1994-01-01	34.42
1995-01-01	35.04
1996-01-01	35.81
1997-01-01	36.57
1998-01-01	37.55
1999-01-01	38.40
2000-01-01	39.93
2001-01-01	40.69
2002-01-01	41.80
2003-01-01	43.23
2004-01-01	44.09
2005-01-01	44.78
2006-01-01	45.70
2007-01-01	46.96
2008-01-01	46.32
2009-01-01	45.81
2010-01-01	46.40
2011-01-01	46.82