Year	per 1,000
1990	5.3
1991	5.2
1992	5.1
1993	5
1994	4.9
1995	4.8
1996	4.7
1997	4.6
1998	4.5
1999	4.4
2000	4.3
2001	4.2
2002	7.3
2003	4.1
2004	4
2005	4
2006	4
2007	4
2008	4
2009	3.9
2010	3.9
2011	3.8
2012	3.7
2013	3.6
2014	3.5
2015	3.4
2016	3.3
2017	3.2
2018	3.1
2019	3
2020	2.9
2021	2.8
2022	2.8