Year	per 1,000
1990	23
1991	22.8
1992	22.6
1993	22.3
1994	22.2
1995	21.9
1996	21.6
1997	21.3
1998	20.8
1999	20.3
2000	19.7
2001	19.2
2002	18.5
2003	17.9
2004	17.3
2005	16.7
2006	16
2007	15.4
2008	14.7
2009	14.1
2010	13.6
2011	13.1
2012	12.6
2013	12.1
2014	11.6
2015	11.2
2016	10.8
2017	10.4
2018	10
2019	9.6
2020	9.2
2021	8.9
2022	8.5