Year	US Dollars adjusted for inflation)
1980	18.67
1981	19.13
1982	19.52
1983	20.06
1984	20.69
1985	21.27
1986	21.48
1987	21.92
1988	22.61
1989	23.02
1990	23.63
1991	24.16
1992	24.6
1993	24.95
1994	26.55
1995	27.01
1996	27.6
1997	27.82
1998	27.71
1999	27.95
2000	28.54
2001	28.38
2002	28.64
2003	29.18
2004	29.7
2005	30.1
2006	30.26