Year	per 1,000
1990	25.8
1991	25.1
1992	24.8
1993	24.4
1994	25.7
1995	22.8
1996	22.2
1997	21.6
1998	20.9
1999	20.2
2000	19.5
2001	18.8
2002	18.1
2003	17.4
2004	16.8
2005	16.1
2006	15.4
2007	14.8
2008	14.2
2009	13.6
2010	13.1
2011	12.6
2012	12.1
2013	11.7
2014	11.3
2015	10.9
2016	10.6
2017	10.3
2018	10
2019	9.8
2020	9.5
2021	9.2
2022	9