Year	Percent
1991	19.979
1992	20.126
1993	19.216
1994	20.344
1995	22.572
1996	21.594
1997	21.628
1998	21.352
1999	21.397
2000	21.633
2001	21.496
2002	17.539
2003	14.097
2004	13.929
2005	14.131
2006	17.347
2007	18.791
2008	19.194
2009	20.524
2010	19.416
2011	17.744
2012	18.077
2013	18.985
2014	18.987
2015	20.193
2016	20.391
2017	20.91
2018	20.525
2019	20.361
2020	20.299
2021	20.326
2022	20.436