Year	Percent
1980	0.261
1981	0.28
1982	0.288
1983	0.297
1984	0.313
1985	0.305
1986	0.327
1987	0.357
1988	0.371
1989	0.366
1990	0.365
1991	0.377
1992	0.359
1993	0.374
1994	0.385
1995	0.381
1996	0.382
1997	0.386
1998	0.354
1999	0.35
2000	0.36
2001	0.354
2002	0.349
2003	0.346
2004	0.357
2005	0.366
2006	0.372
2007	0.376
2008	0.373
2009	0.365
2010	0.37
2011	0.373
2012	0.367
2013	0.366
2014	0.364
2015	0.361
2016	0.357
2017	0.357
2018	0.355
2019	0.354
2020	0.352
2021	0.35
2022	0.348
2023	0.346
2024	0.344