Year	Percent
1991	19.584
1992	20.347
1993	20.706
1994	20.197
1995	20.389
1996	20.541
1997	20.336
1998	20.753
1999	20.685
2000	19.85
2001	20.407
2002	19.294
2003	18.025
2004	18.684
2005	20.5
2006	20.86
2007	20.482
2008	20.667
2009	20.537
2010	21.1
2011	20.153
2012	20.499
2013	20.661
2014	20.662
2015	20.842
2016	21.153
2017	19.962
2018	19.886
2019	20.194
2020	20.288
2021	20.388
2022	20.493