Year Measure 1971 402.40185 1972 400.70133 1973 398.79044 1974 398.78279 1975 407.06338 1976 401.6687 1977 417.77201 1978 419.24615 1979 422.43427 1980 424.14851 1981 431.98875 1982 438.24896 1983 440.03427 1984 440.48051 1985 443.55301 1986 436.30952 1987 430.82544 1988 430.99518 1989 433.51843 1990 425.16068 1991 416.9874 1992 409.69339 1993 412.25481 1994 415.14578 1995 411.374 1996 410.80872 1997 411.97788 1998 413.40221 1999 406.30475 2000 413.09162 2001 407.36184 2002 406.30515 2003 411.83483 2004 413.51545 2005 404.94954 2006 375.59751 2007 344.63615 2008 338.24474 2009 355.79588 2010 348.85465 2011 327.19926 2012 328.43759 2013 336.00359 2014 341.86267