Year	per 1,000
1990	53.8
1991	51
1992	48.3
1993	45.6
1994	43
1995	40.4
1996	38
1997	35.7
1998	33.4
1999	31.4
2000	29.3
2001	27.3
2002	25.4
2003	23.6
2004	21.7
2005	19.9
2006	18.1
2007	16.4
2008	14.8
2009	13.3
2010	11.9
2011	10.6
2012	9.5
2013	8.4
2014	7.5
2015	6.7
2016	6
2017	5.4
2018	5
2019	4.6
2020	4.3
2021	4.1
2022	3.9