Year	per 1,000
1990	6
1991	6
1992	6
1993	6
1994	5.9
1995	5.9
1996	5.8
1997	5.7
1998	5.6
1999	5.5
2000	5.4
2001	5.3
2002	5.1
2003	5
2004	4.8
2005	4.7
2006	4.5
2007	4.3
2008	15.5
2009	3.8
2010	3.6
2011	3.3
2012	3.1
2013	2.8
2014	2.6
2015	2.5
2016	2.3
2017	2.2
2018	2.1
2019	2.1
2020	2
2021	1.9
2022	1.9