Year	US Dollars adjusted for inflation)
1980	19.99
1981	20.32
1982	20.47
1983	21.35
1984	22.76
1985	23.29
1986	24.7
1987	24.62
1988	26.05
1989	27.74
1990	27.2
1991	28.76
1992	28.8
1993	29.52
1994	30.21
1995	29.6
1996	29.68
1997	30.56
1998	31.31
1999	32.37
2000	33.34
2001	32.25
2002	32.78
2003	33.02
2004	34.06
2005	34.73
2006	34.73