Year	Percent
1990	20.86
1991	20.581
1992	20.393
1993	20.249
1994	20.121
1995	19.869
1996	19.491
1997	19.12
1998	18.763
1999	18.427
2000	18.202
2001	17.859
2002	17.672
2003	17.572
2004	17.518
2005	17.472
2006	17.43
2007	17.396
2008	17.373
2009	17.399
2010	17.547
2011	17.61
2012	17.778
2013	18.01
2014	18.251
2015	18.472
2016	18.602
2017	18.627
2018	18.656
2019	18.686
2020	18.714
2021	18.739
2022	18.762
2023	18.786
2024	18.81
2025	18.836
2026	18.86
2027	18.885
2028	18.911
2029	18.936
2030	18.959