Year	Percent (Units)
1980	0.023
1981	0.023
1982	0.023
1983	0.023
1984	0.023
1985	0.023
1986	0.022
1987	0.022
1988	0.026
1989	0.030
1990	0.029
1991	0.030
1992	0.028
1993	0.028
1994	0.026
1995	0.026
1996	0.026
1997	0.025
1998	0.027
1999	0.025
2000	0.026
2001	0.025
2002	0.024
2003	0.023
2004	0.022
2005	0.023
2006	0.024
2007	0.021
2008	0.022
2009	0.024
2010	0.025
2011	0.025
2012	0.028
2013	0.026
2014	0.026
2015	0.020
2016	0.018
2017	0.019
2018	0.018
2019	0.017
2020	0.017
2021	0.016
2022	0.016
2023	0.016
2024	0.016
2025	0.016
2026	0.016
2027	0.016
2028	0.016
2029	0.017