Year	per 1,000
1990	12.3
1991	11.9
1992	11.4
1993	10.9
1994	10.5
1995	10.1
1996	9.6
1997	9.2
1998	8.8
1999	8.5
2000	8.1
2001	7.8
2002	7.4
2003	7.1
2004	6.8
2005	6.5
2006	6.2
2007	6
2008	5.7
2009	5.5
2010	5.3
2011	5.1
2012	4.9
2013	4.7
2014	4.5
2015	4.4
2016	4.2
2017	4
2018	3.9
2019	3.8
2020	3.7
2021	3.6
2022	3.5