Year	per 1,000
1990	3.4
1991	3.3
1992	3.1
1993	2.9
1994	2.8
1995	2.7
1996	2.6
1997	2.6
1998	2.5
1999	2.4
2000	2.3
2001	2.2
2002	2
2003	1.9
2004	11.1
2005	1.8
2006	1.7
2007	1.7
2008	1.7
2009	4.7
2010	1.6
2011	1.5
2012	1.4
2013	1.3
2014	1.1
2015	1
2016	1
2017	0.9
2018	0.9
2019	0.8
2020	0.8
2021	0.7
2022	0.7