Year	per 1,000
1990	6.4
1991	6.3
1992	6.2
1993	6.1
1994	6
1995	6
1996	6
1997	6
1998	6
1999	6
2000	6
2001	6
2002	6
2003	6
2004	8.4
2005	6
2006	5.9
2007	5.9
2008	5.9
2009	5.8
2010	5.8
2011	5.8
2012	5.7
2013	5.6
2014	5.5
2015	5.3
2016	5.2
2017	5.1
2018	5
2019	4.9
2020	4.7
2021	4.6
2022	4.5