Year Percent (Units) 1980 0.002 1981 0.002 1982 0.002 1983 0.002 1984 0.002 1985 0.002 1986 0.003 1987 0.003 1988 0.003 1989 0.003 1990 0.003 1991 0.003 1992 0.002 1993 0.002 1994 0.003 1995 0.002 1996 0.002 1997 0.002 1998 0.002 1999 0.002 2000 0.003 2001 0.002 2002 0.002 2003 0.002 2004 0.002 2005 0.002 2006 0.003 2007 0.003 2008 0.003 2009 0.002 2010 0.002 2011 0.002 2012 0.002 2013 0.002 2014 0.002 2015 0.002 2016 0.002 2017 0.002 2018 0.002 2019 0.002 2020 0.001 2021 0.001 2022 0.001 2023 0.001 2024 0.002 2025 0.002 2026 0.002 2027 0.002 2028 0.002 2029 0.002