Year	%
1981	33.7
1986	23.1
1989	33.3
1990	33
1991	34.3
1992	33.7
1993	33.7
1994	35.3
1995	33.8
1996	34.3
1997	33.8
1998	34
1999	35.9
2000	35.7
2001	39.7
2002	40.4
2003	37
2004	36.6
2005	35.9
2006	38.3
2007	38.9
2008	37.7
2009	39.4
2010	36.8
2011	36.9
2012	36.6
2013	37
2014	36.9
2015	36.8
2016	37.3
2017	37
2018	36.4
2019	36.7
2020	37
2021	37.2
2022	35.7