Year Percent 1980 0.007 1981 0.008 1982 0.007 1983 0.007 1984 0.007 1985 0.007 1986 0.007 1987 0.007 1988 0.007 1989 0.007 1990 0.007 1991 0.007 1992 0.006 1993 0.006 1994 0.006 1995 0.006 1996 0.005 1997 0.006 1998 0.006 1999 0.006 2000 0.005 2001 0.005 2002 0.005 2003 0.005 2004 0.004 2005 0.004 2006 0.004 2007 0.004 2008 0.004 2009 0.004 2010 0.004 2011 0.004 2012 0.004 2013 0.003 2014 0.003 2015 0.003 2016 0.003 2017 0.003 2018 0.003 2019 0.003 2020 0.003 2021 0.003 2022 0.003 2023 0.003 2024 0.003