Year	US Dollars adjusted for inflation)
1980	20.85
1981	20.84
1982	20.94
1983	22.06
1984	22.85
1985	23.18
1986	23.71
1987	24.01
1988	24.56
1989	25.16
1990	25.55
1991	25.9
1992	26.09
1993	26.46
1994	27.42
1995	27.75
1996	27.99
1997	28.49
1998	29.07
1999	29.73
2000	30.27
2001	30.47
2002	30.67
2003	31.09
2004	32.12
2005	32.76
2006	32.96