Year	%
1981	18.4
1982	18.3
1983	18.1
1984	18.1
1985	19.7
1986	18.2
1987	18.1
1988	17.5
1989	16.8
1990	17.9
1992	20.8
1993	17.5
1995	17.9
1996	18.2
1997	18.1
1998	17.9
1999	18
2001	18.5
2002	18.3
2003	18.7
2004	18.8
2005	18.7
2006	18.8
2007	19.2
2008	19.3
2009	19.4
2011	19.5
2012	19.2
2013	19.3
2014	19.5
2015	19.6
2016	19.3
2017	19.4
2018	19.3
2019	19.5
2020	19.3
2021	19.6
2022	19.5