Year	%
1980	30.2
1986	32.2
1987	34.3
1991	36.6
1992	34.3
1993	33.2
1994	34.4
1995	37
1996	36.9
1997	36.4
1998	38.1
1999	37
2000	37.7
2001	39.5
2002	40.5
2003	37.8
2004	35.3
2005	35
2006	33.8
2007	33.7
2008	32.5
2009	31.3
2010	31.8
2011	31
2012	29.8
2013	29.5
2014	30.1
2016	30.7
2017	30
2018	30.1
2019	31.3
2020	30.6
2021	31.2
2022	29.8