Year Measure 1971 3128.60199 1972 3224.51944 1973 3343.35449 1974 3464.06609 1975 3539.87937 1976 3631.2608 1977 3780.58945 1978 3929.15703 1979 3967.23813 1980 3983.84277 1981 3872.53656 1982 3754.67958 1983 3767.59667 1984 3932.19243 1985 4015.15217 1986 3979.67418 1987 4074.77905 1988 4106.15043 1989 4083.66222 1990 4024.66907 1991 3606.58244 1992 3410.72788 1993 3334.79435 1994 3260.63182 1995 3315.04799 1996 3364.25879 1997 3361.88402 1998 3256.50253 1999 3271.41393 2000 3292.60901 2001 3456.70547 2002 3483.86751 2003 3468.78367 2004 3416.24785 2005 3504.47559 2006 3469.29139 2007 3320.45472 2008 3405.69297 2009 3106.68617 2010 3306.80554 2011 3213.94977 2012 3080.72503 2013 3130.92657 2014 2943.18916 2015 3003.66422