Year	per 1,000
1990	5.7
1991	5.3
1992	5
1993	4.7
1994	4.4
1995	4.2
1996	3.9
1997	3.7
1998	20.1
1999	3.4
2000	3.3
2001	3.1
2002	3
2003	2.9
2004	2.8
2005	2.7
2006	2.7
2007	2.6
2008	2.5
2009	2.4
2010	2.4
2011	2.3
2012	2.3
2013	2.3
2014	2.2
2015	2.2
2016	2.1
2017	2.1
2018	2
2019	2
2020	1.9
2021	1.9
2022	1.8