Year	per 1,000
1990	11.4
1991	11.3
1992	11.2
1993	11.1
1994	11
1995	10.9
1996	10.8
1997	10.8
1998	12.1
1999	10.6
2000	10.5
2001	10.4
2002	10.3
2003	10.2
2004	10.1
2005	10
2006	9.9
2007	9.8
2008	9.7
2009	9.6
2010	9.5
2011	9.4
2012	9.3
2013	9.1
2014	9
2015	8.9
2016	8.8
2017	8.6
2018	8.5
2019	8.4
2020	8.2
2021	8.1
2022	8