Year	per 1,000
1990	12.7
1991	12.4
1992	12.1
1993	11.8
1994	11.6
1995	11.3
1996	11
1997	10.8
1998	10.5
1999	10.3
2000	10.1
2001	9.9
2002	9.7
2003	9.5
2004	9.3
2005	9.1
2006	9
2007	8.8
2008	8.7
2009	8.5
2010	8.4
2011	8.2
2012	8.1
2013	7.9
2014	7.8
2015	7.6
2016	7.5
2017	7.3
2018	7.1
2019	7
2020	6.8
2021	6.7
2022	6.5