Year	per 1,000
1990	9.4
1991	9.3
1992	9.3
1993	9.5
1994	9.8
1995	10.1
1996	10.4
1997	10.7
1998	10.9
1999	11
2000	10.9
2001	10.6
2002	10.2
2003	9.8
2004	9.3
2005	8.9
2006	8.4
2007	8
2008	7.6
2009	7.2
2010	6.9
2011	6.5
2012	6.1
2013	5.8
2014	5.4
2015	5
2016	4.7
2017	4.3
2018	4.1
2019	3.8
2020	3.7
2021	3.5
2022	3.4