Year	per 1,000
1990	3.4
1991	3.3
1992	3.1
1993	3
1994	2.9
1995	2.8
1996	2.7
1997	2.6
1998	2.5
1999	2.4
2000	2.4
2001	2.3
2002	2.2
2003	2.1
2004	2
2005	1.9
2006	1.8
2007	1.7
2008	1.7
2009	1.6
2010	1.6
2011	1.5
2012	1.5
2013	1.5
2014	1.4
2015	1.4
2016	1.4
2017	1.4
2018	1.3
2019	1.3
2020	1.2
2021	1.2
2022	1.1