Year	Percent
1991	18.787
1992	18.434
1993	18.317
1994	18.06
1995	17.808
1996	17.701
1997	17.091
1998	16.649
1999	16.21
2000	15.845
2001	16.157
2002	19.715
2003	17.257
2004	18.687
2005	17.243
2006	17.458
2007	17.67
2008	17.524
2009	17.501
2010	18.719
2011	17.546
2012	17.659
2013	18.529
2014	18.183
2015	18.282
2016	18.309
2017	18.061
2018	17.962
2019	17.837
2020	17.735
2021	17.642
2022	17.555