Year	per 1,000
1990	42.9
1991	40.4
1992	38.1
1993	35.9
1994	33.8
1995	31.7
1996	29.8
1997	28
1998	26.2
1999	24.5
2000	22.9
2001	21.4
2002	20.1
2003	18.8
2004	17.6
2005	16.5
2006	15.5
2007	14.4
2008	13.4
2009	12.5
2010	11.7
2011	11
2012	10.4
2013	9.9
2014	9.5
2015	9.1
2016	8.8
2017	8.4
2018	8.1
2019	7.9
2020	7.6
2021	7.3
2022	7.1