Year	per 1,000
1990	4.3
1991	4.1
1992	3.9
1993	3.8
1994	3.6
1995	3.4
1996	3.2
1997	3.1
1998	2.9
1999	2.8
2000	2.6
2001	2.5
2002	2.3
2003	2.2
2004	2
2005	1.9
2006	1.8
2007	1.7
2008	1.6
2009	1.5
2010	1.4
2011	1.3
2012	1.2
2013	1.1
2014	1.1
2015	1
2016	1
2017	0.9
2018	0.9
2019	0.9
2020	0.8
2021	0.8
2022	0.8