Year	per 1,000
1990	3.3
1991	3.1
1992	2.8
1993	2.6
1994	2.4
1995	2.2
1996	2.2
1997	2.3
1998	2.3
1999	2.3
2000	2.3
2001	2.2
2002	2.1
2003	2.1
2004	2
2005	1.9
2006	1.8
2007	1.7
2008	1.5
2009	1.4
2010	1.2
2011	1.1
2012	1
2013	0.9
2014	0.9
2015	0.9
2016	0.9
2017	0.9
2018	0.9
2019	0.8
2020	0.8
2021	0.9
2022	0.9