Year	per 1,000
1990	9.8
1991	9.8
1992	9.8
1993	9.7
1994	9.7
1995	9.7
1996	9.7
1997	9.7
1998	9.7
1999	9.7
2000	9.6
2001	9.6
2002	9.6
2003	9.5
2004	9.5
2005	9.4
2006	9.4
2007	9.3
2008	9.2
2009	9.2
2010	9.1
2011	9
2012	8.9
2013	8.8
2014	8.7
2015	8.6
2016	8.5
2017	8.4
2018	8.3
2019	8.2
2020	8
2021	7.9
2022	7.7