Year	per 1,000
1990	27.2
1991	25.9
1992	24.7
1993	23.6
1994	22.5
1995	21.4
1996	20.4
1997	19.4
1998	18.5
1999	17.6
2000	16.8
2001	16
2002	15.2
2003	14.5
2004	13.9
2005	13.3
2006	12.7
2007	12.2
2008	11.7
2009	11.3
2010	10.8
2011	10.4
2012	10
2013	9.6
2014	9.3
2015	8.9
2016	8.6
2017	8.3
2018	7.9
2019	7.6
2020	7.4
2021	7.1
2022	6.8