Year	%
1971	1.7
1973	2.1
1975	2.2
1977	2.2
1979	2.3
1981	2.5
1982	2.5
1984	2.4
1985	2.5
1986	2.6
1987	2.7
1988	2.8
1989	2.7
1990	2.6
1991	2.5
1992	2.7
1993	2.6
1994	2.7
1995	2.7
1996	2.8
1997	2.8
1998	2.7
1999	2.7
2000	2.7
2001	2.7
2002	2.7
2003	2.7
2004	2.6
2005	2.6
2006	2.7
2007	2.7
2008	2.7
2009	2.7
2010	2.7
2011	2.8
2012	2.5
2013	2.4
2014	2.6
2015	2.5
2016	2.8
2017	2.7
2018	2.8
2019	2.9