Year	%
1997	28.1
1998	30.1
1999	34.4
2000	28.5
2001	29.8
2002	27.5
2003	27.7
2004	27.7
2005	28.4
2006	27.4
2007	26.8
2008	27.1
2009	25
2010	25.4
2011	24.5
2012	23.6
2013	23.3
2014	22.1
2015	22.5
2016	22.7
2017	21.7
2018	22
2019	22
2021	22.1