Year	Percent
1991	18.477
1992	18.827
1993	19.229
1994	19.329
1995	19.015
1996	19.453
1997	18.721
1998	19.044
1999	18.21
2000	17.73
2001	16.835
2002	16.908
2003	16.994
2004	17.049
2005	17.553
2006	17.654
2007	17.45
2008	17.037
2009	17.703
2010	17.332
2011	17.503
2012	17.585
2013	18.811
2014	17.886
2015	18.771
2016	18.471
2017	18.486
2018	18.402
2019	18.318
2020	18.239
2021	18.16
2022	18.081