Year Measure 1971 492.39644 1972 487.96442 1973 513.14715 1974 522.27669 1975 526.55157 1976 548.12241 1977 585.04119 1978 548.51642 1979 448.89536 1980 472.24662 1981 471.54504 1982 469.26889 1983 476.35999 1984 510.5432 1985 520.70871 1986 508.65689 1987 502.38286 1988 464.81275 1989 487.67171 1990 487.16765 1991 505.71245 1992 509.83948 1993 490.88913 1994 485.78093 1995 489.80384 1996 489.41527 1997 503.04472 1998 497.21991 1999 496.19206 2000 500.64375 2001 497.68975 2002 508.74078 2003 513.80083 2004 530.30348 2005 531.93298 2006 520.11344 2007 521.87227 2008 520.87083 2009 517.26623 2010 515.21292 2011 526.60482 2012 559.27184 2013 591.87954 2014 609.00712