Year	US Dollars adjusted for inflation)
1980	20.09
1981	20.4
1982	20.63
1983	21.26
1984	22.13
1985	22.72
1986	23.2
1987	23.69
1988	24.46
1989	25.35
1990	26.4
1991	27.49
1992	27.8
1993	28.25
1994	29.01
1995	30.08
1996	31.05
1997	32.07