Year	per 1,000
1990	6.5
1991	5.9
1992	5.4
1993	5.1
1994	4.9
1995	4.8
1996	4.8
1997	4.8
1998	4.8
1999	4.8
2000	4.9
2001	5.1
2002	5.2
2003	5.3
2004	5.2
2005	5
2006	4.8
2007	4.6
2008	4.4
2009	4.4
2010	4.4
2011	4.4
2012	4.3
2013	4.2
2014	4
2015	3.8
2016	3.8
2017	3.8
2018	3.8
2019	3.9
2020	4.1
2021	4.2
2022	4.4