Year	%
1997	15.8
1998	15.3
1999	14.1
2000	15.8
2001	15.3
2002	16
2003	15.9
2004	16.1
2005	15.8
2006	16.1
2007	16.3
2008	16.1
2009	16.6
2010	16.6
2011	16.9
2012	17.1
2013	17.3
2014	17.4
2015	17.5
2016	17.4
2017	17.6
2018	17.5
2019	17.5
2021	17.6