Year	per 1,000
1990	45.1
1991	38.6
1992	38
1993	37
1994	35.8
1995	34.4
1996	32.9
1997	31.3
1998	29.6
1999	33.2
2000	26.4
2001	24.8
2002	23.4
2003	22
2004	20.7
2005	19.4
2006	18.2
2007	17.1
2008	15.9
2009	14.8
2010	13.8
2011	12.9
2012	12
2013	11.2
2014	10.5
2015	9.8
2016	9.4
2017	9
2018	8.8
2019	8.7
2020	8.6
2021	8.5
2022	8.4