Year	%
1987	35.5
1994	36.9
1995	37
1996	35.6
2000	33
2002	32.3
2003	32.9
2004	33.6
2005	33.8
2006	32.7
2007	31.9
2008	30.9
2009	32.7
2010	32.3
2011	32.9
2012	33.2
2013	33.5
2014	31.9
2015	31.8
2016	32.8
2017	31.4
2018	30.6
2019	30.8
2020	29.2
2021	30.1