Year	Percent (Units)
1980	0.019
1981	0.016
1982	0.017
1983	0.019
1984	0.019
1985	0.020
1986	0.021
1987	0.021
1988	0.021
1989	0.021
1990	0.021
1991	0.022
1992	0.021
1993	0.020
1994	0.020
1995	0.019
1996	0.019
1997	0.019
1998	0.020
1999	0.019
2000	0.018
2001	0.020
2002	0.021
2003	0.023
2004	0.029
2005	0.030
2006	0.029
2007	0.029
2008	0.029
2009	0.030
2010	0.032
2011	0.031
2012	0.029
2013	0.026
2014	0.027
2015	0.030
2016	0.028
2017	0.026
2018	0.027
2019	0.027
2020	0.028
2021	0.026
2022	0.026
2023	0.026
2024	0.026
2025	0.026
2026	0.026
2027	0.026
2028	0.026
2029	0.026