Year Percent (Units) 1980 0.002 1981 0.002 1982 0.002 1983 0.002 1984 0.002 1985 0.003 1986 0.003 1987 0.003 1988 0.003 1989 0.003 1990 0.003 1991 0.003 1992 0.003 1993 0.003 1994 0.003 1995 0.003 1996 0.003 1997 0.003 1998 0.003 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 0.002 2008 0.003 2009 0.003 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 0.002 2021 0.002 2022 0.002 2023 0.002 2024 0.002 2025 0.002 2026 0.002 2027 0.002 2028 0.002 2029 0.002