Year	per 1,000
1990	11.3
1991	11.5
1992	11.7
1993	11.8
1994	11.9
1995	11.8
1996	11.8
1997	11.6
1998	11.3
1999	11
2000	10.6
2001	10.1
2002	9.6
2003	9.1
2004	8.6
2005	8.1
2006	7.7
2007	7.3
2008	7
2009	6.6
2010	6.3
2011	6
2012	5.8
2013	5.5
2014	5.2
2015	4.8
2016	4.5
2017	4.2
2018	3.8
2019	3.5
2020	3.2
2021	3
2022	2.8