Year	Percent (Units)
1980	0.021
1981	0.020
1982	0.019
1983	0.017
1984	0.018
1985	0.018
1986	0.018
1987	0.017
1988	0.017
1989	0.018
1990	0.018
1991	0.017
1992	0.015
1993	0.012
1994	0.014
1995	0.016
1996	0.015
1997	0.015
1998	0.014
1999	0.014
2000	0.013
2001	0.013
2002	0.013
2003	0.013
2004	0.012
2005	0.011
2006	0.011
2007	0.011
2008	0.011
2009	0.011
2010	0.011
2011	0.012
2012	0.012
2013	0.012
2014	0.012
2015	0.013
2016	0.013
2017	0.013
2018	0.013
2019	0.013
2020	0.014
2021	0.014
2022	0.014
2023	0.014
2024	0.015
2025	0.015
2026	0.015
2027	0.016
2028	0.016
2029	0.016