Year	per 1,000
1990	6.4
1991	11.2
1992	7.7
1993	7.5
1994	6.7
1995	5.8
1996	5
1997	4.4
1998	4.1
1999	3.8
2000	3.7
2001	3.6
2002	3.6
2003	3.5
2004	3.5
2005	3.4
2006	3.3
2007	3.3
2008	3.1
2009	3
2010	2.8
2011	2.6
2012	2.4
2013	2.3
2014	2.2
2015	2.1
2016	2.1
2017	2
2018	2
2019	2
2020	2
2021	2
2022	2