Year	per 1,000
1990	11.7
1991	11.8
1992	11.9
1993	12
1994	12
1995	12
1996	12
1997	11.9
1998	11.7
1999	11.4
2000	11.2
2001	10.8
2002	10.5
2003	11.3
2004	9.9
2005	9.6
2006	9.3
2007	9
2008	8.7
2009	8.5
2010	8.4
2011	8.2
2012	8.1
2013	8
2014	9.2
2015	9.4
2016	8
2017	8
2018	7.9
2019	7.9
2020	7.8
2021	7.7
2022	7.5