Year	%
1997	40.8
1998	43.6
1999	43.6
2000	36.8
2001	39.1
2002	42.1
2003	42.2
2004	38
2005	38.5
2006	38.2
2007	37.8
2008	35.4
2009	35.2
2010	34.2
2011	33.5
2012	33.3
2013	32.7
2014	32.1
2015	32.6
2016	32.6
2017	32.3
2018	31.6
2019	31.1
2020	32.9
2021	30.5
2022	30.7