Year	per 1,000
1990	2.9
1991	3
1992	3.2
1993	3.3
1994	3.4
1995	3.5
1996	3.6
1997	3.6
1998	3.6
1999	3.5
2000	3.4
2001	3.3
2002	3.2
2003	3
2004	2.8
2005	2.6
2006	2.4
2007	2.2
2008	1.9
2009	1.8
2010	1.6
2011	1.5
2012	1.4
2013	1.4
2014	1.3
2015	1.3
2016	1.2
2017	1.1
2018	1.1
2019	1
2020	1
2021	0.9
2022	0.8