Year	per 1,000
1990	9.2
1991	9
1992	8.9
1993	8.7
1994	8.6
1995	8.5
1996	8.4
1997	8.3
1998	8.3
1999	8.2
2000	8.2
2001	8.2
2002	8.2
2003	8.1
2004	8.1
2005	8
2006	7.9
2007	7.9
2008	7.8
2009	7.7
2010	7.7
2011	7.6
2012	7.5
2013	7.5
2014	7.4
2015	7.4
2016	7.3
2017	7.2
2018	7
2019	6.9
2020	6.7
2021	6.5
2022	6.3