Year	per 1,000
1990	5.9
1991	5.6
1992	5.4
1993	5.1
1994	4.9
1995	4.6
1996	4.4
1997	4.2
1998	4
1999	3.8
2000	3.6
2001	3.4
2002	3.2
2003	3.1
2004	2.9
2005	2.8
2006	2.7
2007	2.5
2008	2.4
2009	2.3
2010	2.2
2011	2.1
2012	2
2013	2
2014	1.9
2015	1.8
2016	1.8
2017	1.7
2018	1.6
2019	1.6
2020	1.5
2021	1.5
2022	1.4