Year	per 1,000
1990	10.3
1991	10.1
1992	9.8
1993	9.6
1994	9.4
1995	9.2
1996	9
1997	8.8
1998	8.6
1999	8.4
2000	8.2
2001	8
2002	9.8
2003	7.6
2004	8.6
2005	7.3
2006	7.1
2007	7
2008	6.8
2009	6.7
2010	6.6
2011	6.5
2012	6.3
2013	6.2
2014	6.1
2015	7.1
2016	5.8
2017	5.8
2018	5.7
2019	5.6
2020	5.6
2021	5.5
2022	5.5