Year	%
1991	41.4
1995	38.8
1996	39.4
1998	40.5
1999	38.6
2000	39
2001	38.6
2002	38.8
2003	37.3
2004	35.6
2005	36.8
2006	35.6
2007	35.7
2008	36.1
2009	36
2010	33.2
2011	32.8
2012	32.6
2013	34.2
2014	32.2
2015	31.8
2016	30.7
2017	29.1
2018	29.4
2019	29.8
2021	29
2022	28.7