Year Measure 1960 4002.32155 1961 4355.45329 1962 4613.97791 1963 4728.75447 1964 5189.29161 1965 5521.18071 1966 5632.19049 1967 6017.97347 1968 6512.91987 1969 7017.88337 1970 7315.98357 1971 7674.29449 1972 8131.93307 1973 8745.48567 1974 8786.44551 1975 9051.5191 1976 9751.54598 1977 9828.34719 1978 10143.43493 1979 10694.29028 1980 10703.40752 1981 11112.30896 1982 11440.23919 1983 12609.02676 1984 13692.98413 1985 14950.32685 1986 14858.36807 1987 15746.25938 1988 15895.8306 1989 15680.86242 1990 15836.03376 1991 15932.92621 1992 15544.41146 1993 15506.8021 1994 15290.616 1995 15475.01348 1996 15434.23039 1997 15410.69913 1998 15522.1335 1999 15470.86807 2000 15681.61527 2001 16020.98031 2002 15709.42967 2003 15360.17889 2004 15420.97314 2005 15430.96395 2006 15262.58727 2007 15257.93575 2008 14869.34898 2009 14143.01101 2010 14934.32696 2011 14030.16315 2012 14289.59509 2013 13870.38991 2014 13480.14822