Year	per 1,000
1990	8
1991	7.3
1992	6.7
1993	6.1
1994	5.6
1995	5.2
1996	4.9
1997	4.6
1998	6
1999	4.3
2000	4.2
2001	4
2002	4
2003	3.9
2004	4
2005	4.1
2006	4.2
2007	4.4
2008	4.5
2009	4.6
2010	4.4
2011	4.2
2012	4
2013	3.7
2014	3.4
2015	3.2
2016	3.2
2017	3.2
2018	3.3
2019	3.5
2020	3.8
2021	4.1
2022	4.3