Year	US Dollars adjusted for inflation)
1980	18.26
1981	18.58
1982	18.67
1983	19.17
1984	19.72
1985	20.2
1986	19.99
1987	20.35
1988	20.27
1989	20.35
1990	20.34
1991	20.96
1992	21.93
1993	22.43
1994	22.67
1995	22.76
1996	23.47
1997	24.28
1998	25.06
1999	25.84
2000	25.39
2001	26.44
2002	27.07
2003	27.51
2004	27.69
2005	27.74
2006	27.94