Year	per 1,000
1990	9.1
1991	9
1992	8.9
1993	8.9
1994	10.3
1995	8.8
1996	8.8
1997	8.8
1998	8.8
1999	8.8
2000	8.7
2001	8.6
2002	8.5
2003	8.3
2004	8.2
2005	7.9
2006	7.7
2007	7.5
2008	7.4
2009	7.1
2010	7
2011	6.8
2012	6.7
2013	6.6
2014	6.5
2015	6.4
2016	6.3
2017	6.2
2018	6.2
2019	6.1
2020	6.1
2021	6
2022	6.1