Year Measure 1971 665.27196 1972 844.6724 1973 866.41555 1974 901.2078 1975 975.73818 1976 1037.68052 1977 949.72341 1978 886.44468 1979 925.48315 1980 976.38638 1981 977.26838 1982 965.61099 1983 907.24896 1984 852.1738 1985 959.47999 1986 893.36195 1987 900.97332 1988 880.02231 1989 906.13115 1990 886.56583 1991 875.60685 1992 803.24872 1993 749.87924 1994 787.7162 1995 829.56828 1996 869.05472 1997 897.01133 1998 865.53137 1999 908.28185 2000 872.83431 2001 840.84273 2002 839.96472 2003 834.26357 2004 805.00811 2005 832.37816 2006 807.58796 2007 698.95451 2008 573.29482 2009 531.04141 2010 546.84273 2011 570.25093 2012 542.72955 2013 557.57393 2014 536.99549