Year	Percent
1991	20.735
1992	19.474
1993	20.441
1994	20.471
1995	20.106
1996	20.134
1997	19.832
1998	19.818
1999	19.598
2000	19.293
2001	20.216
2002	19.378
2003	17.91
2004	17.779
2005	17.656
2006	16.566
2007	16.31
2008	15.957
2009	16.519
2010	16.456
2011	15.639
2012	15.912
2013	15.905
2014	15.768
2015	15.762
2016	15.704
2017	15.678
2018	15.666
2019	15.656
2020	15.645
2021	15.627
2022	15.608