Year	per 1,000
1990	9.9
1991	7.5
1992	7.1
1993	7.1
1994	7.3
1995	7.7
1996	7.7
1997	7.5
1998	7.2
1999	6.8
2000	6.4
2001	6.2
2002	6.2
2003	6.3
2004	6.7
2005	7.1
2006	7.4
2007	7.5
2008	7.4
2009	7.3
2010	7.1
2011	6.7
2012	6.5
2013	6.7
2014	7.4
2015	8.1
2016	8.1
2017	7.4
2018	6.3
2019	5.2
2020	4.3
2021	3.8
2022	3.5