Year	per 1,000
1990	13.3
1991	13
1992	12.8
1993	12.6
1994	12.4
1995	12.2
1996	11.9
1997	11.7
1998	11.5
1999	11.3
2000	11
2001	10.8
2002	10.6
2003	10.4
2004	10.2
2005	10
2006	9.9
2007	9.8
2008	9.6
2009	9.5
2010	9.5
2011	9.5
2012	9.6
2013	9.7
2014	9.8
2015	9.8
2016	9.9
2017	10
2018	10
2019	9.9
2020	9.9
2021	9.7
2022	9.6