Year	Percent
1991	21.078
1992	20.831
1993	20.685
1994	20.397
1995	20.529
1996	20.739
1997	21.037
1998	26.059
1999	26.125
2000	26.156
2001	26.274
2002	26.5
2003	26.508
2004	26.689
2005	26.89
2006	27.054
2007	27.269
2008	27.431
2009	28.136
2010	27.766
2011	26.536
2012	22.211
2013	21.841
2014	21.968
2015	21.301
2016	20.081
2017	19.562
2018	18.791
2019	18.536
2020	18.748
2021	19.35
2022	19.338