Year	per 1,000
1990	5
1991	5.2
1992	5.3
1993	5.4
1994	5.6
1995	5.6
1996	5.7
1997	5.7
1998	5.7
1999	5.6
2000	5.5
2001	5.3
2002	5.2
2003	5
2004	4.8
2005	4.6
2006	4.4
2007	4.3
2008	4.1
2009	4
2010	3.8
2011	3.7
2012	3.6
2013	3.5
2014	3.3
2015	3.1
2016	3
2017	2.8
2018	2.6
2019	2.4
2020	2.3
2021	2.1
2022	2