Year	per 1,000
1990	30
1991	28
1992	26.1
1993	24.4
1994	22.8
1995	21.2
1996	19.8
1997	18.5
1998	17.3
1999	16.2
2000	15.1
2001	14.1
2002	13.2
2003	12.2
2004	11.3
2005	10.5
2006	9.7
2007	8.9
2008	8.1
2009	7.4
2010	6.7
2011	6.1
2012	5.5
2013	5
2014	4.5
2015	4.1
2016	3.7
2017	3.4
2018	3.1
2019	2.9
2020	2.7
2021	2.6
2022	2.5