Year	per 1,000
1990	9.4
1991	9.3
1992	9.3
1993	9.3
1994	9.3
1995	9.3
1996	9.2
1997	9.2
1998	9.1
1999	9
2000	8.9
2001	8.8
2002	8.6
2003	8.4
2004	8.3
2005	8.1
2006	7.9
2007	7.7
2008	7.4
2009	7.3
2010	7.1
2011	6.9
2012	6.7
2013	6.6
2014	6.4
2015	6.3
2016	6.1
2017	6
2018	5.8
2019	5.7
2020	5.5
2021	5.4
2022	5.3