Year	per 1,000
1990	4.3
1991	4.2
1992	4.1
1993	4
1994	3.9
1995	3.8
1996	3.7
1997	3.6
1998	3.5
1999	3.4
2000	3.4
2001	3.3
2002	3.2
2003	3.1
2004	5.7
2005	2.9
2006	2.9
2007	2.8
2008	2.7
2009	2.6
2010	2.6
2011	2.5
2012	2.5
2013	2.4
2014	2.4
2015	2.3
2016	2.3
2017	2.2
2018	2.2
2019	2.1
2020	2.1
2021	2
2022	2