Year Measure 1971 2637.66077 1972 3033.69237 1973 2952.73515 1974 2992.76532 1975 3801.40257 1976 4136.08228 1977 4976.89689 1978 6314.64967 1979 8703.78398 1980 9710.64686 1981 9929.71823 1982 10010.95906 1983 9515.99301 1984 9556.16406 1985 10062.49309 1986 10273.11199 1987 9828.55086 1988 9623.83448 1989 9513.49947 1990 9587.67539 1991 8986.83258 1992 9834.1732 1993 10365.53514 1994 10757.35316 1995 10739.01316 1996 11837.93346 1997 12078.00856 1998 13800.11991 1999 14027.64436 2000 14353.32375 2001 15006.01408 2002 15760.64145 2003 16228.90968 2004 16231.03228 2005 15467.1896 2006 15702.97175 2007 15192.92084 2008 14457.20348 2009 14232.64059 2010 14821.23712 2011 14761.37443 2012 15462.40747 2013 14445.4077 2014 15309.42938