Year	per 1,000
1990	5.9
1991	5.7
1992	5.6
1993	5.5
1994	5.4
1995	5.4
1996	5.5
1997	5.5
1998	5.6
1999	5.6
2000	5.5
2001	5.3
2002	5.1
2003	4.9
2004	4.7
2005	4.7
2006	4.6
2007	4.6
2008	4.7
2009	4.7
2010	4.6
2011	4.5
2012	4.3
2013	4.1
2014	3.9
2015	3.7
2016	3.6
2017	3.4
2018	3.3
2019	3.3
2020	3.4
2021	3.7
2022	4.2