Year	per 1,000
1990	8.2
1991	8.2
1992	8.2
1993	8.1
1994	8
1995	7.8
1996	7.5
1997	7.3
1998	7
1999	6.8
2000	6.5
2001	6.3
2002	6.1
2003	5.9
2004	5.8
2005	7.6
2006	5.6
2007	5.6
2008	5.5
2009	5.5
2010	5.4
2011	5.3
2012	5.2
2013	5.1
2014	5
2015	4.9
2016	4.8
2017	4.7
2018	4.6
2019	4.4
2020	4.3
2021	4.2
2022	4.1