Year Percent 1991 4.066 1992 2.889 1993 2.363 1994 1.971 1995 2.083 1996 2.446 1997 2.707 1998 2.489 1999 2.396 2000 2.472 2001 2.283 2002 2.319 2003 2.3 2004 2.553 2005 2.59 2006 2.66 2007 2.666 2008 2.957 2009 2.464 2010 2.763 2011 2.643 2012 2.558 2013 2.398 2014 2.47 2015 2.19 2016 2.258 2017 2.31 2018 2.309 2019 2.312 2020 2.321 2021 2.326 2022 2.328