Year	per 1,000
1990	9.7
1991	10.8
1992	3.5
1993	3.6
1994	3.6
1995	3.6
1996	3.6
1997	3.6
1998	3.6
1999	3.5
2000	3.4
2001	3.3
2002	3.2
2003	3
2004	2.9
2005	2.8
2006	2.7
2007	2.6
2008	2.5
2009	2.4
2010	2.4
2011	2.4
2012	2.4
2013	2.5
2014	2.6
2015	2.7
2016	2.8
2017	2.8
2018	2.9
2019	2.9
2020	2.9
2021	2.9
2022	2.9