Year	per 1,000
1990	17.5
1991	16.4
1992	15.3
1993	14.4
1994	13.6
1995	12.7
1996	11.9
1997	11.2
1998	10.5
1999	9.9
2000	9.3
2001	8.8
2002	8.4
2003	8
2004	7.6
2005	7.2
2006	6.8
2007	6.4
2008	6.1
2009	8.1
2010	5.5
2011	5.2
2012	5
2013	4.8
2014	4.7
2015	4.6
2016	4.4
2017	4.3
2018	4.2
2019	4.2
2020	4.1
2021	4.1
2022	4