Year	US Dollars adjusted for inflation)
1980	14.09
1981	14.79
1982	15.37
1983	16.1
1984	17.22
1985	17.9
1986	18.3
1987	18.55
1988	18.89
1989	19.34
1990	19.73
1991	20
1992	20.69
1993	21.5
1994	22.17
1995	22.24
1996	22.21
1997	22.24
1998	22.11
1999	21.91
2000	21.87
2001	21.87
2002	22.08
2003	21.86
2004	21.73
2005	21.67
2006	21.69