Year	Percent (Units)
1980	0.289
1981	0.300
1982	0.258
1983	0.245
1984	0.249
1985	0.245
1986	0.250
1987	0.257
1988	0.263
1989	0.281
1990	0.280
1991	0.295
1992	0.295
1993	0.308
1994	0.314
1995	0.330
1996	0.334
1997	0.345
1998	0.349
1999	0.337
2000	0.337
2001	0.340
2002	0.341
2003	0.343
2004	0.348
2005	0.351
2006	0.354
2007	0.354
2008	0.357
2009	0.354
2010	0.356
2011	0.364
2012	0.371
2013	0.371
2014	0.367
2015	0.361
2016	0.353
2017	0.355
2018	0.357
2019	0.349
2020	0.338
2021	0.353
2022	0.349
2023	0.339
2024	0.335
2025	0.333
2026	0.331
2027	0.328
2028	0.326
2029	0.324