Year	per 1,000
1990	6.9
1991	6.8
1992	6.7
1993	6.6
1994	6.5
1995	6.5
1996	6.4
1997	6.3
1998	6.2
1999	6.2
2000	6.1
2001	6.1
2002	6
2003	6
2004	6
2005	5.9
2006	5.9
2007	5.9
2008	5.8
2009	5.8
2010	5.7
2011	5.7
2012	5.6
2013	5.6
2014	5.5
2015	5.4
2016	5.4
2017	5.3
2018	5.3
2019	5.2
2020	5.2
2021	5.1
2022	5.1