Year	per 1,000
1990	5.8
1991	5.5
1992	5.3
1993	5
1994	4.8
1995	4.5
1996	4.2
1997	3.9
1998	3.7
1999	3.4
2000	3.1
2001	2.9
2002	2.7
2003	2.5
2004	2.4
2005	2.3
2006	2.2
2007	2.1
2008	2
2009	1.9
2010	1.8
2011	1.8
2012	1.7
2013	1.7
2014	1.6
2015	1.6
2016	1.5
2017	1.5
2018	1.5
2019	1.5
2020	1.6
2021	1.7
2022	1.7