Year	%
1980	34.5
1985	34.4
1990	32
1993	35.7
1994	35.1
1995	35.7
1996	36.5
1997	35.3
1998	34.6
1999	33.8
2000	34.1
2003	31.8
2004	33.3
2005	32.4
2006	33.5
2007	34.1
2008	34.2
2009	34.9
2010	35.2
2011	35.7
2012	35.4
2013	36.2
2014	36.1
2015	36.2
2016	35.8
2017	34.7
2018	34.7
2019	34.3
2020	34.9
2021	33.9