Year	Percent
1991	19.553
1992	19.03
1993	18.258
1994	17.448
1995	16.804
1996	17.277
1997	17.937
1998	18.546
1999	19.073
2000	19.475
2001	19.407
2002	19.326
2003	19.284
2004	19.209
2005	19.118
2006	19.208
2007	19.196
2008	19.149
2009	18.738
2010	18.365
2011	18.315
2012	18.347
2013	18.109
2014	17.814
2015	17.443
2016	16.839
2017	16.655
2018	16.424
2019	16.181
2020	15.937
2021	15.78
2022	15.724