Year	per 1,000
1990	5.7
1991	5.5
1992	5.1
1993	4.9
1994	4.6
1995	4.4
1996	4.2
1997	4
1998	3.8
1999	3.6
2000	3.5
2001	3.4
2002	3.2
2003	3
2004	3.4
2005	2.7
2006	2.6
2007	2.4
2008	3.2
2009	2.2
2010	2.1
2011	2
2012	1.9
2013	1.9
2014	1.7
2015	1.7
2016	1.6
2017	1.6
2018	1.5
2019	1.4
2020	1.4
2021	1.3
2022	1.3