Year	per 1,000
1990	11.1
1991	11
1992	10.9
1993	10.8
1994	10.7
1995	10.6
1996	10.5
1997	10.4
1998	10.3
1999	10.2
2000	10.1
2001	10
2002	9.9
2003	9.8
2004	9.7
2005	9.6
2006	9.5
2007	9.4
2008	9.3
2009	9.3
2010	9.2
2011	9.1
2012	9.1
2013	9
2014	8.9
2015	8.9
2016	8.8
2017	8.8
2018	8.7
2019	8.6
2020	8.5
2021	8.3
2022	8.1