Year	per 1,000
1990	3.6
1991	3.7
1992	3.6
1993	3.6
1994	3.5
1995	3.4
1996	3.3
1997	3.3
1998	3.2
1999	3.1
2000	3
2001	2.9
2002	2.7
2003	2.6
2004	2.4
2005	2.2
2006	2.1
2007	2
2008	2
2009	1.9
2010	1.9
2011	1.8
2012	1.7
2013	1.7
2014	1.6
2015	1.6
2016	1.6
2017	1.5
2018	1.5
2019	1.5
2020	1.5
2021	1.5
2022	1.6