Year	per 1,000
1990	14
1991	14
1992	13.8
1993	13.6
1994	13.4
1995	13.1
1996	12.9
1997	12.5
1998	12.2
1999	11.8
2000	11.4
2001	11
2002	10.5
2003	10
2004	9.5
2005	8.9
2006	8.3
2007	7.7
2008	14.1
2009	6.5
2010	6
2011	5.5
2012	5
2013	4.6
2014	4.2
2015	3.9
2016	3.7
2017	3.5
2018	3.4
2019	3.3
2020	3.2
2021	3.1
2022	3