Year % 1988 19.92692 1989 19.82393 1990 20.70909 1991 21.09525 1992 21.82608 1993 21.10551 1994 21.55904 1995 25.32895 1996 27.00101 1997 24.32491 1998 22.74358 1999 23.80952 2000 22.87207 2001 22.77237 2002 23.75642 2003 23.98119 2004 24.32842 2005 24.16673 2006 25.5092 2007 25.20298 2008 25.0102 2009 25.47043 2010 24.60505 2011 27.12906 2012 25.7997 2013 18.9545 2014 27.63286 2015 26.11097 2016 27.16157 2017 30.72602 2018 29.71416 2019 26.61177 2020 25.47803 2021 25.08456