Year	per 1,000
1990	13.2
1991	13.3
1992	13.3
1993	13.2
1994	13
1995	12.7
1996	12.2
1997	11.7
1998	11.1
1999	10.4
2000	9.7
2001	8.9
2002	8.2
2003	7.5
2004	6.9
2005	6.3
2006	5.7
2007	5.2
2008	4.7
2009	4.3
2010	3.9
2011	3.5
2012	3.2
2013	2.9
2014	2.6
2015	2.3
2016	2.1
2017	1.9
2018	1.8
2019	1.6
2020	1.5
2021	1.5
2022	1.4