Year	Percent (Units)
1980	0.269
1981	0.288
1982	0.295
1983	0.305
1984	0.322
1985	0.313
1986	0.336
1987	0.367
1988	0.381
1989	0.376
1990	0.375
1991	0.387
1992	0.370
1993	0.385
1994	0.397
1995	0.392
1996	0.393
1997	0.397
1998	0.364
1999	0.360
2000	0.370
2001	0.364
2002	0.359
2003	0.356
2004	0.368
2005	0.377
2006	0.383
2007	0.388
2008	0.385
2009	0.377
2010	0.382
2011	0.386
2012	0.370
2013	0.364
2014	0.360
2015	0.367
2016	0.360
2017	0.361
2018	0.358
2019	0.343
2020	0.330
2021	0.330
2022	0.307
2023	0.308
2024	0.307
2025	0.306
2026	0.304
2027	0.303
2028	0.301
2029	0.300