Year	per 1,000
1990	23.1
1991	21.7
1992	20.5
1993	19.4
1994	18.3
1995	17.3
1996	16.3
1997	15.5
1998	14.7
1999	13.8
2000	13.1
2001	12.3
2002	11.6
2003	10.8
2004	10.1
2005	9.4
2006	8.7
2007	8
2008	7.4
2009	6.8
2010	6.3
2011	5.8
2012	5.3
2013	5
2014	4.7
2015	4.4
2016	4.2
2017	4
2018	3.9
2019	6.1
2020	3.6
2021	3.4
2022	3.3