Year	per 1,000
1990	11.3
1991	11.2
1992	11.2
1993	11.2
1994	11.2
1995	11.3
1996	11.4
1997	11.5
1998	11.6
1999	11.8
2000	11.9
2001	11.9
2002	11.9
2003	11.7
2004	11.5
2005	11.2
2006	11
2007	10.6
2008	10.3
2009	10
2010	9.7
2011	9.4
2012	9.2
2013	9
2014	8.7
2015	8.4
2016	8.2
2017	7.9
2018	7.7
2019	7.4
2020	7.2
2021	7
2022	6.8