Year	%
1997	22.5
1998	22
1999	20.3
2000	22
2001	21.7
2002	22.5
2003	21.8
2004	21.8
2005	21.9
2006	22.5
2007	22.4
2008	22.2
2009	23
2010	22.4
2011	22.4
2012	22.3
2013	22.4
2014	22.5
2015	22.3
2016	21.9
2017	22.3
2018	22.1
2019	22.3
2021	22.1