Year	%
1981	33.3
1989	32.2
1992	31.4
1995	30.5
1996	30.4
1997	31.2
1998	31.7
2000	32.2
2001	33.7
2002	34.2
2003	34.3
2004	34.7
2005	33.6
2006	35
2007	35.4
2008	34.3
2009	34.6
2010	33.6
2011	31.6
2012	29.2
2013	30.1
2014	29.8
2015	29.8
2016	29.6
2017	29.6
2018	29.7
2019	29.7
2020	29.9
2021	30.8
2022	30.5