Year	per 1,000
1990	13.7
1991	13.3
1992	13
1993	12.6
1994	12.3
1995	12
1996	11.6
1997	11.4
1998	11.1
1999	10.8
2000	10.5
2001	10.2
2002	10
2003	9.7
2004	9.4
2005	9.1
2006	8.9
2007	8.6
2008	8.3
2009	7.9
2010	7.6
2011	7.3
2012	7
2013	6.6
2014	6.4
2015	6.1
2016	5.8
2017	5.6
2018	5.4
2019	5.2
2020	5
2021	4.8
2022	4.7