Year % 1985 82.54912 1986 82.28424 1987 83.62853 1988 79.50002 1989 80.13357 1990 81.06621 1991 82.10541 1992 83.21922 1993 84.17584 1994 85.20342 1995 86.13851 1996 86.97314 1997 87.77018 1998 88.66835 1999 89.42835 2000 88.595 2001 90.70417 2002 88.86428 2003 90.25422 2004 89.69637 2005 90.78618 2006 92.12294 2007 91.05315 2008 91.24999 2009 90.92858 2010 90.43022 2011 91.93887 2012 90.84885 2013 91.14488 2016 91.25275 2017 92.23703