Year	per 1,000
1990	5
1991	4.8
1992	4.6
1993	4.6
1994	4.5
1995	4.5
1996	4.4
1997	4.2
1998	3.8
1999	3.4
2000	3.1
2001	2.8
2002	2.6
2003	2.5
2004	2.4
2005	2.3
2006	2.3
2007	2.3
2008	2.3
2009	2.3
2010	2.2
2011	2.1
2012	1.9
2013	1.8
2014	1.7
2015	1.6
2016	1.6
2017	1.6
2018	1.6
2019	1.7
2020	1.7
2021	1.8
2022	1.8