Year	US Dollars adjusted for inflation)
1987	11.93
1988	13
1989	13.6
1990	14.38
1991	14.15
1992	15
1993	14.69
1994	15.62
1995	17.08
1996	17.19
1997	17.61
1998	18.14
1999	18.25
2000	18.75
2001	17.82
2002	18.03
2003	17.9
2004	18.07
2005	18.33
2006	18.72