Year	per 1,000
1990	13.3
1991	13.1
1992	13
1993	12.9
1994	12.9
1995	12.9
1996	12.9
1997	12.9
1998	12.9
1999	12.9
2000	12.9
2001	12.9
2002	12.9
2003	12.9
2004	12.9
2005	12.9
2006	12.9
2007	12.8
2008	12.6
2009	12.3
2010	13.7
2011	13.4
2012	11.4
2013	11.1
2014	10.8
2015	10.5
2016	10.3
2017	10
2018	9.8
2019	9.5
2020	9.3
2021	9.1
2022	8.8