Year	Percent (Units)
1980	0.020
1981	0.020
1982	0.020
1983	0.020
1984	0.020
1985	0.020
1986	0.020
1987	0.020
1988	0.020
1989	0.020
1990	0.020
1991	0.020
1992	0.019
1993	0.019
1994	0.020
1995	0.020
1996	0.020
1997	0.020
1998	0.020
1999	0.020
2000	0.020
2001	0.020
2002	0.021
2003	0.020
2004	0.019
2005	0.019
2006	0.019
2007	0.019
2008	0.019
2009	0.019
2010	0.019
2011	0.019
2012	0.018
2013	0.019
2014	0.018
2015	0.019
2016	0.021
2017	0.024
2018	0.024
2019	0.025
2020	0.027
2021	0.027
2022	0.027
2023	0.028
2024	0.028
2025	0.029
2026	0.029
2027	0.030
2028	0.031
2029	0.032