Year	Percent
1968	0.9
1969	0.4
1970	0.4
1971	0.9
1972	0.9
1973	0.8
1974	0.8
1975	1.2
1976	1.6
1977	1.6
1978	1.5
1979	1.5
1980	1.4
1981	1.7
1982	1.7
1983	1.7
1984	1.7
1985	1.7
1986	1.3
1987	1.3
1988	1.2
1989	0.9
1990	0.8
1991	1
1992	1
1993	1
1994	1.4
1995	1.3
1996	1.5
1997	1.5
1998	2.1
1999	2.2
2000	2.28
2001	2.45
2002	2.14
2003	2.43
2004	2.14
2005	2.03
2006	2.11
2007	1.91
2008	2.12
2009	2.53
2010	2.52
2011	2.19
2012	2.26
2013	2.3
2014	2.2
2015	2
2016	1.9
2017	1.8
2018	1.5
2019	1.5
2020	1.7