Year	US Dollars adjusted for inflation)
1980	9.99
1981	10.51
1982	10.09
1983	9.61
1984	9.55
1985	9.35
1986	8.71
1987	8.57
1988	8.38
1989	8.41
1990	8.53
1991	8.6
1992	8.71
1993	8.75
1994	8.82
1995	8.37
1996	7.92
1997	8.17
1998	8.36
1999	8.19
2000	8.73
2001	8.83
2002	8.57
2003	8.74
2004	8.8
2005	8.83
2006	9.19