Year	%
1970	15.3
1975	15.7
1979	16.4
1984	16.7
1990	16.8
1996	17.1
1997	17.1
1998	17.1
1999	16.9
2000	16.9
2001	16.9
2002	16.9
2003	16.8
2004	17
2005	17.2
2006	17.3
2007	16.5
2008	16.5
2009	16.7
2010	16.3
2011	16.4
2012	16.5
2013	16.6
2014	16.7
2015	16.7
2016	16.9
2017	16.9
2018	16.7
2019	17.3
2020	17.5
2021	17.3