Year	Percent
1991	17.962
1992	17.845
1993	17.422
1994	17.596
1995	17.768
1996	17.914
1997	18.124
1998	18.301
1999	18.342
2000	17.983
2001	18.113
2002	17.281
2003	17.424
2004	17.407
2005	17.656
2006	17.897
2007	18.001
2008	18.104
2009	18.144
2010	17.984
2011	18.248
2012	18.495
2013	18.571
2014	18.959
2015	18.852
2016	18.664
2017	18.598
2018	18.601
2019	18.602
2020	18.595
2021	18.594
2022	18.598