Year Percent 1990 16.16 1991 16.61 1992 16.68 1993 16 1994 15.89 1995 15.64 1996 15.36 1997 15.39 1998 15.18 1999 14.87 2000 14.4 2001 13.75 2002 13.16 2003 13 2004 12.92 2005 12.73 2006 12.95 2007 12.95 2008 13.05 2009 13.14 2010 13.33 2011 13.1 2012 13.38 2013 13.83 2014 14.52 2015 15.3 2016 15.92 2017 15.887 2018 15.854 2019 15.82 2020 15.787 2021 15.754 2022 15.721 2023 15.687 2024 15.654 2025 15.621 2026 15.588 2027 15.555 2028 15.521 2029 15.488 2030 15.455