Year	per 1,000
1990	9.7
1991	9.5
1992	9.4
1993	9.2
1994	9
1995	8.9
1996	8.7
1997	8.6
1998	8.4
1999	8.3
2000	8.1
2001	8
2002	7.9
2003	7.7
2004	7.6
2005	7.4
2006	7.2
2007	7
2008	6.8
2009	6.6
2010	6.5
2011	6.4
2012	6.3
2013	6.2
2014	6.1
2015	6.1
2016	6.1
2017	6.1
2018	6.1
2019	6.1
2020	6.1
2021	6.1
2022	6