Year	Percent
1991	20.714
1992	20.507
1993	20.41
1994	20.218
1995	20.158
1996	20.019
1997	19.662
1998	19.373
1999	19.103
2000	18.887
2001	18.777
2002	18.727
2003	18.559
2004	18.414
2005	18.201
2006	17.982
2007	17.931
2008	17.922
2009	18.235
2010	18.406
2011	18.381
2012	18.401
2013	18.335
2014	18.29
2015	18.188
2016	18.148
2017	18.115
2018	18.084
2019	18.028
2020	17.952
2021	17.857
2022	17.757