Year % 1988 15.13533 1989 15.71462 1990 20.88422 1991 21.1868 1992 20.77558 1993 17.21824 1994 17.74051 1995 24.90896 1996 31.28151 1997 28.44493 1998 22.96523 1999 18.91264 2000 18.55474 2001 21.59943 2002 21.35761 2003 21.93359 2004 18.66892 2005 17.18664 2006 20.97429 2007 20.77506 2008 17.29213 2009 16.56008 2010 18.11398 2011 16.5732 2012 17.05898 2013 16.65655 2014 19.09314 2015 19.38812 2016 18.67354 2017 18.64967 2018 17.85365 2019 18.68754 2020 5.649583 2021 18.19871