Year US Dollars adjusted for inflation) 1970 16860 1971 16750 1972 15790 1973 16640 1974 13590 1975 11360 1976 11700 1977 12480 1978 13970 1979 17210 1980 18050 1981 17190 1982 17660 1983 18510 1984 18530 1985 18950 1986 19020 1987 19930 1988 20060 1989 22220 1990 20640 1991 19720 1992 17950 1993 17390 1994 17740 1995 17110 1996 16740 1997 16620 1998 16710 1999 18430 2000 19090 2001 18530 2002 18380 2003 18380 2004 18710