Year	per 1,000
1990	8.2
1991	8.8
1992	9.3
1993	9.6
1994	9.7
1995	9.5
1996	9.3
1997	8.9
1998	8.6
1999	8.2
2000	7.9
2001	7.5
2002	7.1
2003	6.6
2004	6.3
2005	5.9
2006	5.5
2007	5.2
2008	4.9
2009	4.6
2010	4.3
2011	4.1
2012	4
2013	3.8
2014	3.8
2015	3.8
2016	3.8
2017	3.7
2018	3.7
2019	3.6
2020	3.5
2021	3.4
2022	3.3