Year	per 1,000
1990	12.1
1991	11.6
1992	11
1993	10.4
1994	9.9
1995	9.4
1996	8.9
1997	8.4
1998	8
1999	7.6
2000	7.2
2001	6.9
2002	6.6
2003	6.3
2004	6
2005	5.8
2006	5.6
2007	5.4
2008	5.2
2009	5
2010	4.8
2011	4.7
2012	4.5
2013	4.4
2014	4.3
2015	4.2
2016	4.1
2017	4
2018	3.9
2019	3.8
2020	3.7
2021	3.6
2022	3.5