Year	%
1981	18.2
1988	14.7
1990	11.4
1992	13.6
1994	12
1996	12.1
1998	12.1
1999	13.4
2000	12.3
2002	12.9
2004	13.8
2006	15
2007	13.1
2008	13.6
2009	13.4
2010	12.4
2011	10.4
2012	12.7
2013	11.8
2014	11.3
2015	10
2016	10.8
2017	11
2018	11.3
2019	9.6
2020	10.6
2021	10