Year	Percent
1990	48.961
1991	49.007
1992	49.003
1993	48.954
1994	48.867
1995	48.746
1996	48.614
1997	48.482
1998	48.345
1999	48.194
2000	48.025
2001	47.891
2002	47.739
2003	47.598
2004	47.515
2005	47.516
2006	47.569
2007	47.702
2008	47.704
2009	48.332
2010	49.62
2011	52.12
2012	51.987
2013	52.646
2014	51.958
2015	51.176
2016	51.211
2017	51.435
2018	51.609
2019	51.731
2020	51.802
2021	51.804
2022	51.758
2023	51.682
2024	51.602
2025	51.53
2026	51.467
2027	51.419
2028	51.386
2029	51.375
2030	51.395