Year	Percent (Units)
1980	0.030
1981	0.030
1982	0.030
1983	0.028
1984	0.023
1985	0.024
1986	0.024
1987	0.023
1988	0.024
1989	0.023
1990	0.022
1991	0.021
1992	0.020
1993	0.019
1994	0.019
1995	0.019
1996	0.018
1997	0.018
1998	0.019
1999	0.018
2000	0.017
2001	0.018
2002	0.018
2003	0.018
2004	0.017
2005	0.018
2006	0.018
2007	0.017
2008	0.018
2009	0.019
2010	0.019
2011	0.019
2012	0.020
2013	0.020
2014	0.020
2015	0.020
2016	0.020
2017	0.020
2018	0.021
2019	0.022
2020	0.023
2021	0.022
2022	0.024
2023	0.024
2024	0.025
2025	0.026
2026	0.027
2027	0.027
2028	0.028
2029	0.029