Year	per 1,000
1990	3.8
1991	3.5
1992	3.3
1993	3.1
1994	2.9
1995	2.7
1996	2.5
1997	3.1
1998	2.3
1999	2.2
2000	2.2
2001	2.1
2002	2
2003	1.9
2004	1.9
2005	1.8
2006	1.7
2007	1.6
2008	1.6
2009	1.5
2010	1.4
2011	1.4
2012	1.3
2013	1.3
2014	1.2
2015	1.1
2016	1.1
2017	1
2018	1
2019	0.9
2020	0.9
2021	0.8
2022	0.8