Year	Percent
1991	18.819
1992	19.967
1993	19.34
1994	19
1995	18.888
1996	18.59
1997	18.694
1998	18.877
1999	18.467
2000	18.203
2001	18.411
2002	18.226
2003	18.134
2004	18.139
2005	19.02
2006	19.902
2007	17.981
2008	15.913
2009	15.558
2010	15.885
2011	15.721
2012	15.457
2013	14.899
2014	14.162
2015	14.619
2016	15.151
2017	15.007
2018	14.999
2019	14.991
2020	14.981
2021	14.968
2022	14.955