Year	%
1980	18.2
1988	20
1989	19.5
1991	20.4
1992	19.4
1996	18.5
1999	18.2
2000	18.1
2001	18.2
2002	18.4
2003	18.8
2004	18.3
2005	18.6
2008	19
2009	19.2
2010	19
2011	19.3
2012	19.7
2013	19.6
2014	19.6
2015	20
2016	19.9
2017	20.1
2018	19.9
2019	19.8
2020	19.5
2021	18.8
2022	18.8