Year	US Dollars adjusted for inflation)
1980	19.71
1981	20.03
1982	20.18
1983	20.55
1984	21.2
1985	21.6
1986	21.5
1987	21.81
1988	21.82
1989	21.55
1990	21.76
1991	22.13
1992	22.94
1993	23.03
1994	23.38
1995	23.75
1996	23.78
1997	24.21
1998	24.88
1999	25.39
2000	25.85
2001	26.53
2002	26.93
2003	26.95
2004	27.07
2005	27.71
2006	27.93