Year	US Dollars adjusted for inflation)
1980	17.24
1981	17.19
1982	17.83
1983	18.58
1984	18.73
1985	19.25
1986	19.51
1987	19.83
1988	20.44
1989	21.15
1990	21.71
1991	22.1
1992	22.26
1993	22.47
1994	23.4
1995	24.76
1996	24.98
1997	26.92
1998	27.66
1999	28.74
2000	29.68
2001	29.81
2002	30.23
2003	30.17
2004	31.19
2005	31.06
2006	31.75