Year	Percent
1991	19.034
1992	18.908
1993	18.442
1994	16.825
1995	16.772
1996	13.491
1997	15.815
1998	16.527
1999	15.728
2000	15.166
2001	15.132
2002	14.686
2003	14.873
2004	14.673
2005	15.398
2006	14.968
2007	15.552
2008	15.796
2009	15.768
2010	15.644
2011	15.888
2012	15.531
2013	15.641
2014	16.084
2015	29.917
2016	19.309
2017	19.227
2018	19.133
2019	19.006
2020	18.88
2021	18.734
2022	18.584