Year	per 1,000
1990	9.6
1991	9.5
1992	9
1993	8.8
1994	8.8
1995	8.2
1996	7.9
1997	7.7
1998	7.5
1999	7.2
2000	7
2001	6.8
2002	6.6
2003	6.4
2004	6.4
2005	6.1
2006	5.9
2007	5.7
2008	5.7
2009	5.3
2010	5.1
2011	4.9
2012	4.7
2013	4.5
2014	4.3
2015	4.2
2016	4
2017	3.9
2018	3.8
2019	3.6
2020	3.5
2021	3.5
2022	3.4