Year	per 1,000
1990	4.4
1991	4.2
1992	3.9
1993	3.7
1994	3.5
1995	3.3
1996	3.1
1997	2.9
1998	2.7
1999	2.5
2000	2.4
2001	2.2
2002	2.1
2003	2
2004	1.9
2005	1.8
2006	1.7
2007	1.6
2008	1.8
2009	1.4
2010	1.3
2011	1.3
2012	1.2
2013	1.2
2014	1.1
2015	1.1
2016	1
2017	1
2018	1
2019	0.9
2020	0.9
2021	0.9
2022	0.8