Year	per 1,000
1990	3.8
1991	3.8
1992	3.8
1993	3.8
1994	3.9
1995	3.9
1996	3.8
1997	3.5
1998	3.2
1999	2.7
2000	2.4
2001	2.1
2002	1.9
2003	1.8
2004	1.7
2005	1.6
2006	1.6
2007	1.6
2008	1.6
2009	1.5
2010	1.5
2011	1.4
2012	1.3
2013	1.2
2014	1.2
2015	1.1
2016	1.1
2017	1.1
2018	1.1
2019	1.1
2020	1.1
2021	1.1
2022	1.1