Year	Percent
1990	20.05
1991	20.036
1992	20.011
1993	19.997
1994	19.929
1995	19.925
1996	19.88
1997	19.777
1998	19.707
1999	19.658
2000	19.562
2001	19.506
2002	19.435
2003	19.386
2004	19.334
2005	19.299
2006	19.331
2007	19.281
2008	19.22
2009	19.146
2010	19.104
2011	19.066
2012	19.032
2013	18.997
2014	18.949
2015	18.877
2016	18.832
2017	18.794
2018	18.757
2019	18.719
2020	18.682
2021	18.644
2022	18.607
2023	18.569
2024	18.531
2025	18.494
2026	18.456
2027	18.419
2028	18.381
2029	18.344
2030	18.306