Year	per 1,000
1990	5.8
1991	5.3
1992	4.9
1993	4.7
1994	4.5
1995	4.5
1996	4.4
1997	4.4
1998	4.3
1999	4.1
2000	4
2001	4
2002	4
2003	3.9
2004	3.8
2005	3.7
2006	3.6
2007	3.4
2008	3.4
2009	3.4
2010	3.5
2011	3.6
2012	3.6
2013	3.6
2014	3.5
2015	3.4
2016	3.4
2017	3.4
2018	3.4
2019	3.5
2020	3.6
2021	3.7
2022	3.7