Year US Dollars adjusted for inflation) 1970 3016 1971 3163 1972 3473 1973 3790 1974 4113 1975 5121 1976 6022 1977 6726 1978 7652 1979 8449 1980 8570 1981 8732 1982 8547 1983 8905 1984 9113 1985 9417 1986 10080 1987 10360 1988 10860 1989 11660 1990 11960 1991 12730 1992 13740 1993 14070 1994 14620 1995 15080 1996 15820 1997 16570 1998 17260 1999 18030 2000 18860 2001 18770 2002 19380 2003 18790 2004 18640