Year	per 1,000
1990	10.9
1991	10.7
1992	10.5
1993	10.3
1994	10.1
1995	9.9
1996	9.7
1997	9.5
1998	9.3
1999	9.1
2000	8.9
2001	8.7
2002	8.5
2003	8.3
2004	8.1
2005	7.8
2006	7.5
2007	7.3
2008	7
2009	6.8
2010	6.5
2011	6.2
2012	6
2013	5.7
2014	5.4
2015	5.2
2016	5
2017	4.7
2018	4.6
2019	4.4
2020	4.2
2021	4.1
2022	4