Year % 1984 91.3022 1985 91.85793 1986 91.21399 1987 91.07816 1988 90.60161 1989 90.98805 1990 91.10368 1991 91.32477 1992 91.46165 1993 92.06101 1994 92.22767 1995 92.80976 1996 93.17284 1997 93.56842 1998 94.40866 1999 95.07321 2000 95.48902 2001 96.07854 2002 96.46903 2003 96.90092 2004 96.91948 2005 96.96806 2006 97.02688 2007 97.14948 2008 97.30175 2009 97.36592 2010 97.55999 2011 97.55328 2012 96.72979 2013 97.20609 2014 97.6273 2015 97.56913 2016 97.56217 2017 97.52933