Year	US Dollars adjusted for inflation)
1980	12.85
1981	12.27
1982	12.47
1983	12.43
1984	13.16
1985	13.25
1986	13.52
1987	13.76
1988	14.19
1989	14.44
1990	14.27
1991	15.03
1992	14.7
1993	14.2
1994	14.45
1995	14.7
1996	14.73
1997	15.44
1998	15.24
1999	15.36
2000	15.73
2001	16.36
2002	16.64
2003	17.05
2004	17.91
2005	18.42
2006	18.98