Year	Percent
1972	1.67
1973	1.55
1974	1.48
1975	2.29
1976	1.76
1977	1.46
1978	1.8
1979	1.99
1980	1.65
1981	2.03
1982	1.7
1983	2.04
1984	2.9
1985	2.32
1986	1.79
1987	2.03
1988	3.02
1989	4.83
1990	5.26
1991	5.41
1992	5.91
1993	5.97
1994	5.35
1995	6.31
1996	5.04
1997	4.69
1998	3.74
1999	3.25
2000	3.46
2001	3.74
2002	4.02
2003	4.22
2004	4.26
2005	4.38
2006	3.4
2007	2.49
2008	2.55
2009	3.1
2010	3.52
2011	3.21
2012	3.12
2013	3.42
2014	3.48
2015	4.3
2016	4.68
2017	4.16
2018	3.8
2019	3.69
2020	4.42