Year	per 1,000
1990	6.1
1991	6
1992	5.9
1993	5.8
1994	5.8
1995	5.8
1996	5.7
1997	5.7
1998	5.7
1999	5.6
2000	5.5
2001	5.5
2002	5.4
2003	5.3
2004	5.2
2005	5.1
2006	5.1
2007	5.1
2008	5.2
2009	5.3
2010	5.9
2011	5.3
2012	5.2
2013	5.2
2014	5.2
2015	5.2
2016	5.2
2017	5.1
2018	4.9
2019	4.8
2020	4.7
2021	4.6
2022	4.5