Year	%
1977	12.1
1978	12.4
1979	12.3
1980	12.3
1981	12.8
1982	13.3
1983	13.2
1984	12.8
1986	12.8
1987	12
1989	12.5
1991	13
1993	12
1995	12
1998	11.9
2000	12.1
2002	12.3
2003	12.1
2004	12.3
2005	12.4
2006	12.4
2007	12.6
2008	12.4
2009	12.4
2010	12.5
2011	12.2
2012	12.3
2013	12.3
2014	12.3
2015	12.1
2016	12.1
2017	12
2018	12.2
2019	12.3
2020	12.1
2021	12.1