Year	%
1997	36.9
1998	39.5
1999	42.6
2000	36.4
2001	38
2002	35.8
2003	34.9
2004	35
2005	36.3
2006	35.4
2007	34.4
2008	34.7
2009	32.9
2010	32.1
2011	30.6
2012	29.2
2013	28.5
2014	26.8
2015	27
2016	26.3
2017	25.9
2018	25.7
2019	26
2021	25.7