Year	per 1,000
1990	13.2
1991	13.3
1992	12.3
1993	11.9
1994	11.5
1995	11.1
1996	10.7
1997	10.3
1998	10
1999	9.5
2000	9.1
2001	8.8
2002	8.5
2003	8.2
2004	8
2005	7.8
2006	7.4
2007	7.1
2008	7.2
2009	6.6
2010	6.4
2011	6
2012	5.7
2013	5.5
2014	5.2
2015	5
2016	4.8
2017	4.6
2018	4.4
2019	4.3
2020	4.1
2021	3.9
2022	3.8