Year	per 1,000
1990	14.2
1991	14
1992	13.9
1993	13.6
1994	13.5
1995	13.3
1996	13.1
1997	12.9
1998	12.7
1999	12.6
2000	12.5
2001	12.4
2002	12.3
2003	12.3
2004	12.2
2005	12.2
2006	12
2007	11.8
2008	11.7
2009	11.4
2010	11.2
2011	10.9
2012	10.6
2013	10.3
2014	10
2015	9.6
2016	9.3
2017	9
2018	8.7
2019	8.5
2020	8.3
2021	8.1
2022	7.8