Year	per 1,000
1990	3.3
1991	3.2
1992	3.1
1993	3
1994	2.9
1995	2.8
1996	2.7
1997	2.6
1998	2.5
1999	2.4
2000	2.3
2001	2.2
2002	2.1
2003	2
2004	1.9
2005	1.8
2006	1.8
2007	1.7
2008	1.6
2009	1.6
2010	1.5
2011	1.5
2012	1.4
2013	1.4
2014	1.3
2015	1.3
2016	1.3
2017	1.2
2018	1.2
2019	1.1
2020	1.1
2021	1.1
2022	1.1