Year	per 1,000
1990	11.9
1991	4.2
1992	4.1
1993	4.1
1994	4
1995	3.9
1996	3.8
1997	3.8
1998	3.7
1999	3.6
2000	3.5
2001	3.5
2002	3.4
2003	3.3
2004	3.2
2005	3.1
2006	4
2007	3
2008	3
2009	2.9
2010	2.9
2011	2.9
2012	2.9
2013	2.9
2014	2.9
2015	2.9
2016	3
2017	3.2
2018	3.1
2019	3.1
2020	3.2
2021	3.3
2022	3.3