Year	Percent
1991	21.065
1992	21.469
1993	19.513
1994	20.437
1995	20.507
1996	19.853
1997	18.749
1998	18.673
1999	18.147
2000	19.875
2001	20
2002	20.337
2003	20.195
2004	19.593
2005	19.837
2006	20.494
2007	20.275
2008	19.902
2009	20.055
2010	20.159
2011	20.434
2012	19.369
2013	19.249
2014	18.518
2015	17.915
2016	17.803
2017	17.623
2018	17.531
2019	17.44
2020	17.359
2021	17.265
2022	17.171