Year	per 1,000
1990	7.8
1991	7.2
1992	6.5
1993	5.8
1994	5.2
1995	4.8
1996	4.4
1997	4.1
1998	3.9
1999	3.7
2000	3.5
2001	3.3
2002	3.1
2003	3
2004	2.8
2005	3.6
2006	2.6
2007	2.5
2008	2.4
2009	2.3
2010	2.2
2011	2.1
2012	2.1
2013	2
2014	1.9
2015	1.9
2016	1.8
2017	1.8
2018	1.7
2019	1.6
2020	1.6
2021	1.5
2022	1.5