Year Percent 1980 0.002 1981 0.002 1982 0.001 1983 0.001 1984 0.002 1985 0.001 1986 0.002 1987 0.002 1988 0.002 1989 0.002 1990 0.002 1991 0.002 1992 0.002 1993 0.003 1994 0.003 1995 0.002 1996 0.002 1997 0.002 1998 0.002 1999 0.003 2000 0.003 2001 0.003 2002 0.003 2003 0.003 2004 0.003 2005 0.003 2006 0.003 2007 0.003 2008 0.003 2009 0.003 2010 0.003 2011 0.003 2012 0.003 2013 0.003 2014 0.003 2015 0.003 2016 0.003 2017 0.003 2018 0.002 2019 0.002 2020 0.002 2021 0.002 2022 0.002 2023 0.002 2024 0.002