Year	Percent (Units)
1980	0.016
1981	0.016
1982	0.015
1983	0.016
1984	0.017
1985	0.017
1986	0.018
1987	0.017
1988	0.016
1989	0.015
1990	0.014
1991	0.013
1992	0.013
1993	0.011
1994	0.006
1995	0.008
1996	0.008
1997	0.009
1998	0.010
1999	0.010
2000	0.010
2001	0.010
2002	0.011
2003	0.011
2004	0.012
2005	0.012
2006	0.012
2007	0.013
2008	0.014
2009	0.015
2010	0.015
2011	0.016
2012	0.016
2013	0.016
2014	0.017
2015	0.018
2016	0.019
2017	0.019
2018	0.020
2019	0.022
2020	0.021
2021	0.022
2022	0.023
2023	0.024
2024	0.025
2025	0.026
2026	0.027
2027	0.028
2028	0.029
2029	0.031