Year	per 1,000
1990	11.2
1991	10.8
1992	10.4
1993	10.1
1994	9.8
1995	9.6
1996	9.3
1997	9.1
1998	8.9
1999	8.6
2000	8.4
2001	8.1
2002	7.9
2003	7.6
2004	7.3
2005	7
2006	6.8
2007	6.5
2008	6.3
2009	6.2
2010	6
2011	5.8
2012	5.7
2013	5.5
2014	5.3
2015	5.2
2016	5
2017	4.9
2018	4.8
2019	4.6
2020	4.5
2021	4.4
2022	4.3