Year	per 1,000
1990	6.5
1991	6.4
1992	6.2
1993	6.1
1994	5.8
1995	5.5
1996	5.2
1997	4.8
1998	4.4
1999	4
2000	3.6
2001	3.2
2002	3
2003	2.7
2004	2.5
2005	2.4
2006	2.3
2007	2.2
2008	2.2
2009	2.1
2010	2.1
2011	2.1
2012	2
2013	2
2014	1.9
2015	1.9
2016	1.8
2017	1.7
2018	1.6
2019	1.5
2020	1.5
2021	1.4
2022	1.3