Year	per 1,000
1990	12.4
1991	12.5
1992	12.6
1993	12.6
1994	12.6
1995	12.6
1996	12.6
1997	12.5
1998	12.4
1999	12.3
2000	12.1
2001	11.9
2002	11.7
2003	11.4
2004	11.1
2005	10.7
2006	10.3
2007	9.8
2008	15
2009	8.8
2010	8.4
2011	7.9
2012	7.5
2013	7
2014	6.6
2015	6.4
2016	6.1
2017	6
2018	5.9
2019	5.8
2020	5.7
2021	5.7
2022	5.6