Year	per 1,000
1990	18
1991	12
1992	11.2
1993	10.8
1994	10.9
1995	11.1
1996	11.3
1997	11.2
1998	11.1
1999	11
2000	10.9
2001	10.9
2002	10.9
2003	11.2
2004	11.6
2005	11.9
2006	11.9
2007	11.6
2008	11
2009	10.3
2010	9.6
2011	8.8
2012	8.3
2013	8.3
2014	8.9
2015	9.6
2016	9.8
2017	9.4
2018	8.6
2019	7.7
2020	6.9
2021	6.4
2022	6.1