Year	%
1997	15.1
1998	15.5
1999	15.5
2000	15.1
2001	14
2002	13.4
2003	15
2004	15.4
2005	15.2
2006	15.5
2007	15.1
2008	14
2009	13.3
2010	13.2
2011	12.9
2012	12.7
2013	12.5
2014	12
2015	11.6
2016	11.8
2017	11.3
2018	10.8
2019	10.9
2020	9.8