Year	Percent
1991	18.053
1992	18.511
1993	19.218
1994	19.796
1995	20.455
1996	21.154
1997	20.822
1998	20.528
1999	20.162
2000	19.908
2001	19.628
2002	19.31
2003	19.041
2004	18.757
2005	18.491
2006	18.237
2007	17.968
2008	17.693
2009	17.391
2010	17.512
2011	17.559
2012	17.703
2013	17.867
2014	17.99
2015	18.128
2016	18.26
2017	18.166
2018	18.081
2019	17.994
2020	17.906
2021	17.82
2022	17.735