Year	per 1,000
1990	13.4
1991	13.8
1992	12.4
1993	11.9
1994	11.5
1995	11
1996	10.5
1997	10
1998	9.5
1999	8.9
2000	8.5
2001	8
2002	7.7
2003	7.3
2004	7.1
2005	7
2006	6.4
2007	6.1
2008	5.8
2009	5.5
2010	5.1
2011	4.7
2012	4.4
2013	4.1
2014	3.8
2015	3.5
2016	3.3
2017	3
2018	2.8
2019	2.6
2020	2.4
2021	2.3
2022	2.2