Year	Percent (Units)
1980	0.019
1981	0.019
1982	0.018
1983	0.015
1984	0.013
1985	0.013
1986	0.012
1987	0.013
1988	0.014
1989	0.014
1990	0.014
1991	0.014
1992	0.012
1993	0.013
1994	0.013
1995	0.013
1996	0.014
1997	0.015
1998	0.016
1999	0.018
2000	0.017
2001	0.019
2002	0.020
2003	0.020
2004	0.021
2005	0.021
2006	0.022
2007	0.023
2008	0.024
2009	0.025
2010	0.025
2011	0.026
2012	0.026
2013	0.027
2014	0.028
2015	0.032
2016	0.033
2017	0.030
2018	0.030
2019	0.030
2020	0.030
2021	0.029
2022	0.030
2023	0.030
2024	0.031
2025	0.031
2026	0.032
2027	0.035
2028	0.038
2029	0.040